Borderline drink driving cases: defence options when you are just over the limit
Breath readings of 36-50 micrograms give your solicitor the most to work with. Procedural errors and calibration issues can get charges dropped. Book your free confidential consultation!
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If your evidential breath test reading was between 36 and 50 micrograms, you have a borderline case. The lower the reading, the more likely a procedural challenge or calibration issue could affect the outcome. Readings in this range are the most defensible drink driving cases because small errors in testing procedure, device calibration, or timing can mean the difference between a conviction and an acquittal.
This page explains what makes borderline cases different, the specific defences that apply at low readings, and what to expect if you have been charged.
What counts as a borderline drink driving reading?
A borderline drink driving reading is an evidential breath test result between 36 and 50 micrograms of alcohol per 100 millilitres of breath. The legal drink driving limit in England and Wales is 35 micrograms, set by section 5 of the Road Traffic Act 1988. A reading of 36 puts you one microgram over. A reading of 50 puts you fifteen over. Both are technically above the limit, but the defence options at these levels are completely different from someone who blew 90 or 120.
At borderline levels, the margin between guilt and innocence is razor thin. The Intoximeter EC/IR, which is the evidential breath testing device used in police stations across England and Wales, has a known calibration tolerance. A reading of 36 could, in certain circumstances, reflect a true breath alcohol level of 34, which is under the limit. The same is true of 37, 38, and readings in that range. The higher you go within the borderline band, the harder this argument becomes, but even at 50 micrograms there are procedural defences that do not apply in the same way to higher readings.
What matters is the gap between your reading and the limit. The smaller that gap, the more weight a court will give to arguments about calibration error, mouth alcohol contamination, and procedural failings. If you are in this range, your case is not hopeless. It may be one of the more winnable cases on that day’s court list.
The timing of the test also matters. Your body eliminates alcohol at a fairly constant rate, typically around 6 to 10 micrograms per hour in breath. If you were tested an hour after you stopped driving, your reading at the time of the test may be lower than your reading at the time of driving. But the reverse is also true: if you were still absorbing alcohol when you were stopped, your reading could be higher at the station than it was behind the wheel. These timing questions are particularly relevant at the borderline, where a few micrograms in either direction change the outcome.
Why borderline cases are different from high-reading cases
At 36 to 50 micrograms, the reading is close enough to the legal limit that procedural and technical defences carry real weight. At 90 micrograms and above, the court’s focus shifts to mitigation and sentence reduction. At borderline, acquittal is a realistic outcome.
The reason is simple mathematics. If your reading is 38 and the Intoximeter’s calibration tolerance means the true value could be 36 or 40, you are in a range where a reasonable doubt exists. If your reading is 110, a calibration tolerance of two or three micrograms either way makes no practical difference to the outcome.
Borderline cases used to trigger a separate right to replace a low breath reading with blood or urine. That “statutory option” was removed in 2015, so a valid evidential breath reading is now normally the evidence the prosecution relies on. The defence focus is therefore the reliability of the breath test itself: the device checks, the two readings, the observation period, possible mouth alcohol, and whether the custody procedure was followed.
At higher readings, the defence strategy is typically about reducing the sentence: arguing for a shorter disqualification, avoiding custody, or securing a drink drive rehabilitation course. At borderline, the strategy is about avoiding conviction altogether. That is a fundamentally different kind of case, and it needs a solicitor who understands the technical and procedural arguments that work at this level. Readings above 90 micrograms are treated differently. See our high reading drink driving page for those cases.
What changed when the statutory option was removed?
Before 2015, some drivers with lower evidential breath readings could require the breath specimen to be replaced by blood or urine. That is no longer the law. If you provided a valid evidential breath specimen, the police do not have to offer you a blood or urine test just because the reading was between 40 and 50 micrograms.
This does not mean low-reading cases cannot be defended. It means the argument has to focus on the breath evidence itself. We check whether the Intoximeter produced two valid readings within tolerance, whether the device checks were recorded, whether the operator followed the required procedure, and whether anything happened during the observation period that could have affected the sample.
Blood or urine samples can still be used in specific situations, for example where a breath specimen cannot be provided for a genuine medical reason, where an evidential breath device is unavailable, or where drugs are also suspected. If blood or urine was used in your case, the sample-taking and continuity procedures still need to be checked carefully.
The practical point is simple: if you were not offered blood or urine after a borderline breath reading, that is not automatically a defence. The better question is whether the breath evidence was reliable and whether the police followed the correct procedure.
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Procedural defences for borderline readings
Procedural defences matter in every drink driving case. In borderline cases they can be decisive, because even a small error in the testing procedure could mean the difference between a reading that is just above the limit and one that is just below it.
The 20-minute observation period is the starting point. Before the evidential breath test at the police station, the officer conducting the test must observe you continuously for at least 20 minutes. During this period they are watching for anything that could affect the accuracy of the sample, such as vomiting, belching, eating, drinking, or smoking. If any of these happen, the 20 minutes must restart. The purpose is to ensure that mouth alcohol, which is alcohol in your mouth rather than in your lungs, has had time to dissipate before you blow into the machine. If the officer left the room during this period, took a phone call, dealt with another detainee, or simply was not paying attention, the observation period may not have been properly completed. In a borderline case, where the reading is only a few micrograms above the limit, mouth alcohol from a recent belch could be exactly the amount that tipped you over. This argument does not carry the same weight when someone blows 90 or above.
Intoximeter calibration is the second area we examine. The machine must produce two readings, and the lower of the two is the one used. The two readings must be within 15% of each other, or within 5 micrograms, whichever is the greater. If the two readings are too far apart, it raises questions about whether the machine was functioning correctly. Even when the two readings are within tolerance, the Intoximeter has a known margin of error. Calibration records, maintenance logs, and the printout from the test itself can all reveal irregularities. For a reading of 37 or 38, a calibration issue of two or three micrograms is enough to take the true reading below the limit.
Mouth alcohol contamination is a specific problem at borderline readings. Residual alcohol in the mouth from mouthwash, breath spray, cough medicine, or certain asthma inhalers can produce a falsely elevated reading. Gastro-oesophageal reflux disease (acid reflux) can also bring alcohol vapour from the stomach back into the mouth. The 20-minute observation period is supposed to guard against this, but if the observation was inadequate, or if the officer did not ask about medical conditions or recent use of mouth products, the reading may not reflect your true deep lung alcohol level. At 38 micrograms, even a tiny amount of residual mouth alcohol could be the difference.
Finally, compliance with the Police and Criminal Evidence Act 1984 (PACE) and Code C must be checked. The custody officer must follow specific procedures when you arrive at the station: explaining your rights, offering legal advice, and ensuring you are fit to provide a sample. If the officer did not explain that you could speak to a solicitor before providing the sample, or if the test was conducted under pressure or while you were unwell, there may be grounds to exclude the evidence under section 78 of PACE. This is a discretionary power, and courts exercise it when admitting the evidence would make the proceedings unfair. We review the custody record, the officer’s statement, and any body-worn camera footage of the testing procedure to identify these issues.
What is the hip flask defence?
The hip flask defence applies when you drank alcohol after driving but before the breath test. If you can prove your blood alcohol was below the limit at the time of driving, the prosecution fails.
The name comes from the idea of someone taking a swig from a hip flask after parking, though the real-world scenarios are usually different. The most common situation is a driver involved in a collision who returns home and has a drink before the police arrive. Another common scenario is someone who parks at home, goes inside, and starts drinking, only for the police to knock on the door an hour later following a report of erratic driving.
The legal basis is section 15(3) of the Road Traffic Offenders Act 1988. The law assumes that your alcohol level at the time of driving was at least as high as at the time of the test. The hip flask defence reverses that assumption. You must prove, on the balance of probabilities, that you consumed alcohol after driving and that without that post-driving alcohol you would have been under the limit.
The evidence you need is specific. Witness testimony from anyone who saw you drink after parking. CCTV footage if you went to a pub or shop. Receipts for alcohol purchases. And, most importantly, a back-calculation from a forensic toxicologist. The toxicologist takes your breath or blood reading at the time of the test, subtracts the estimated contribution from the alcohol you consumed after driving, and calculates what your level would have been when you were behind the wheel. They factor in your body weight, the type and quantity of alcohol, and the rate at which your body absorbs and eliminates it.
This defence succeeds more often than people expect, but it depends entirely on the quality of the evidence. Vague claims that you “had a drink when you got home” are not enough. You need to be specific about what you drank, how much, and when. If the evidence is there, it is a complete defence to the charge. For more on our approach, see our drink driving solicitors page.
Penalties if convicted of a borderline drink driving offence
If you are convicted of drink driving with a borderline reading, the penalties are at the lower end of the scale, but they are still serious. A conviction means a criminal record, a driving ban, and a fine.
The Sentencing Council guidelines place readings of 36 to 59 micrograms in Band A, the lowest category for drink driving. The starting point is a Band C fine, with a normal range of 125% to 175% of weekly income. The minimum disqualification for Band A is 12 months, with an upper range of 16 months. There is no prospect of custody at this level, and a community order would be unusual unless there were aggravating factors such as an accident or children in the car.
If the court offers you a drink drive rehabilitation course, completing it can reduce your disqualification by up to 25%. On a 12-month ban, that means you could be back on the road in 9 months. The course is not automatic. The court must offer it at the point of sentence, and you must pay for it yourself, typically around 200 to 250 pounds.
In exceptional circumstances, the court can impose 10 penalty points instead of a disqualification, but this is rare. It is generally reserved for cases where losing your licence would cause exceptional hardship, and you must make a formal application to the court.
The long-term impact of a conviction goes beyond the ban itself. Your motor insurance premiums will increase significantly for at least five years. You will need to declare the conviction on certain job applications. And the conviction stays on your driving record for 11 years. For the full breakdown of how courts sentence drink driving cases across all reading levels, see our drink driving penalties page and our sentencing guidelines page.
How Scarsdale Solicitors defends borderline cases
When we take on a borderline case, we start by obtaining the full prosecution evidence pack. That includes the Intoximeter printout showing both readings, the calibration check, and the time stamps. It includes the custody record, the arresting officer’s statement, and any body-worn camera footage from the stop and the testing procedure. We also request the station’s Intoximeter maintenance log and the officer’s training records for the device.
We check every step of the procedure against what the law requires. Was the 20-minute observation period completed without interruption? Were your PACE rights explained? Was the Intoximeter functioning correctly, and were the two readings within the required tolerance?
For borderline cases where the evidence supports a technical challenge, we instruct independent forensic toxicologists. A toxicologist can analyse the Intoximeter readings, consider the timing of the test relative to when you were driving, and assess whether mouth alcohol or other factors could have inflated the reading. Their expert report can be the difference between a conviction and a case that the prosecution decides not to pursue.
We operate on fixed fees, so you know the cost before you commit. Our initial consultation is free and confidential. We are regulated by the Solicitors Regulation Authority (SRA number 629410). Our director, Shazia Ali, has over 20 years of experience in motoring law. We are based in Rochdale, Greater Manchester, but we attend magistrates’ courts and Crown Courts across England and Wales. If you are facing a borderline drink driving charge, we can assess the strength of the prosecution evidence and tell you honestly whether you have a defence worth running. Visit our about us page or see our fees page for full pricing.
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We also provide expert legal representation across multiple practice areas throughout England and Wales. Moreover, our experienced team delivers specialist advice with a proven high success rate in motoring cases. Therefore, whatever legal challenge you face, we have the expertise to help.
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Our motoring law specialists defend all driving-related charges with exceptional results. Specifically, we handle:
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Furthermore, our drink driving defence includes specialist support for:
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Additionally, our drug driving expertise covers:
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Moreover, we defend all “failing to” offences including:
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Consequently, our comprehensive motoring defence also includes:
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Furthermore, our Immigration Solicitors guide individuals and businesses through complex visa applications, sponsorship licences, and settlement matters. Consequently, we ensure compliance and maximize approval chances.
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Frequently Asked Questions
Common Questions About Borderline Drink Driving Cases
A borderline reading is between 36 and 50 micrograms of alcohol per 100 millilitres of breath. The legal limit is 35 micrograms. Readings in this range are close enough to the limit that small procedural errors or calibration tolerances on the Intoximeter can affect whether the charge is sustainable.
Yes. The police must follow strict procedures including a 20-minute continuous observation period before the evidential test. If that observation was interrupted, if mouth alcohol from a recent belch or use of a mouth spray contaminated the sample, or if the device was not properly calibrated, the reading may be unreliable. At borderline levels, these arguments carry the most weight because even a small error can take the true reading below the limit.
No. The old statutory option was removed in 2015. If you provided a valid evidential breath specimen, the police do not have to offer blood or urine just because the reading was low. Blood or urine may still be used where breath cannot be provided, a device is unavailable, or drugs are also suspected.
The Intoximeter EC/IR has a known calibration tolerance, and readings can be affected by ambient temperature, radio frequency interference, and residual mouth alcohol. The device must be properly maintained and calibrated. If maintenance records show irregularities, or if the two evidential readings are significantly different from each other, the reliability of the result can be challenged.
If the police did not follow the required procedures, the evidential breath test result may be excluded under section 78 of the Police and Criminal Evidence Act 1984. This includes failures in the 20-minute observation period, device-check problems, and not explaining your right to legal advice. Without admissible breath test evidence, the prosecution cannot prove the charge.
Your Licence, Your Livelihood, Your Future
Don’t let a borderline drink driving charge destroy your life unnecessarily. Moreover, with expert legal defence from Scarsdale Solicitors’ drink driving borderline cases solicitors, many drivers with marginal readings walk away with complete acquittals—no ban, no criminal record, no consequences.
If you have been charged with drink driving and your reading was between 36 and 50 micrograms, speak to us before your first court date. We will review the prosecution evidence, identify any procedural or technical issues, and give you an honest assessment of your options. If this is your first offence, there may be additional strategies we can use. For advice on keeping your licence, we can discuss exceptional hardship applications as well.
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