How do I know if I've had too much to drink when driving?

By MAJ Law on 17 June 2024

Truthfully, the only way of knowing whether you've had too much to drink is to carry a breathalyser around with you - except these are notoriously unreliable unless they are of police standard. The other way is to just not drink at all. This is because it is impossible to say how much a single person can drink and still be under the drink drive limit.

As a general rule, alcohol is broken down by the liver at a rate of around 1 unit per hour, plus 1 hour for absorption. But you cannot take this as gospel since factors such as age, weight, gender, and amount of food eaten can affect how fast the body can process alcohol. No two people will be exactly the same, so where one can have 3 pints and drive, another may only be able to have 1. The rate of alcohol absorption cannot be increased by sleeping, drinking water or sucking a penny (a common myth)! About 10% of alcohol is eliminated through breath, sweat and urine.

The chart below is not intended to help you work out how much you can ‘get away’ with drinking before driving. It is intended simply to give you some understanding of alcohol elimination rates and timings of alcohol absorption. You may be surprised by the results.

What is the UK drink driving limit?

In England and Wales, the alcohol limit for drivers is 80 milligrams of alcohol per 100 millilitres of blood, 35 microgrammes per 100 millilitres of breath or 107 milligrammes per 100 millilitres of urine. In most other European countries, the limit is less, usually 50 milligrammes per 100 millilitres of blood (around 22 microgrammes).

The drink driving limit is not set at the point in which a motorist is deemed to be ‘drunk’. In fact, many of those arrested for this offence will often report feeling ‘completely fine’. The drink driving limit in England and Wales is set at the point that a motorist’s reactions are deemed to be dangerously slow.

Many of the functions that we depend on to drive safely are affected when we drink alcohol. Alcohol can cause;

Hazy thinking
Slowed reaction time
Dulled hearing
Impaired vision
Weakened muscles

How Long Does Alcohol Stay in Your System?

Depending on the body system and test used, alcohol detection times may vary. Alcohol detection tests used by police forces can measure alcohol in the breath for 12 to 24 hours. The table below contains some standard rules of alcohol elimination.

Body System	Time in System
Blood	Up to 6 Hours
Breath	12-24 Hours
Urine	12-24 Hours
Saliva (not used by police)	12-24 Hours
Hair (not used by police)	Up to 90 Days

If you're stopped and arrested on suspicion of drink driving, you are likely to be breath tested. The legal limit for alcohol in the UK is 35 microgrammes (ug). However, the police do not prosecute until 40ug to allow for unreliable readings or over-estimations.

An evidential breath test machine has to be correctly maintained by the police. This means regular servicing and recalibration. Often, due to miscommunication and poor training, the police fail to correctly maintain breath machines. Remember that you can always ask the police to provide calibration data (this includes maintenance logs and service records).

Five things you should know about drink driving

1. Drink driving carries a mandatory driving ban. The minimum disqualification period is 12 months, but this will increase depending upon the alcohol level. In more serious cases, you can get community service or be sent to prison. See the sentencing guidelines below:

Sentencing Guidelines
Driving or attempting to drive:

Triable only summarily
Maximum: Unlimited fine and/or 6 months

Must endorse and disqualify for at least 12 months.
Must disqualify for at least 2 years if offender has had two or more disqualifications for periods of 56 days or more in preceding 3 years – refer to disqualification guidance. Magistrates: consult your legal adviser for further guidance
Must disqualify for at least 3 years if offender has been convicted of a relevant offence in preceding 10 years – consult your legal adviser for further guidance If there is a delay in sentencing after conviction, consider interim disqualification

2. The court have recently began using alcohol monitoring tags as part of a community penalty. These tags are locked to your ankle and measure alcohol levels throughout the day. If the tag detects alcohol, the court can send you to prison.

3. Just because you were over the limit does not mean that you are guilty. Procedure plays an important part in a drink driving case and can help you avoid a conviction (see below)

4. Drink driving breath machines are not always accurate. Have you seen calibration records and maintenance logs?

5. There is generally no legal aid for drink driving offences. Specialist representation may not cost you as much as you think. You can find out more about solicitors costs by calling us today on (see bottom of the page for contact number).

Are there any defences?

Yes.

Just because you've been charged does not mean that you are guilty of the offence - even if you think you are. We're often called by people who find themselves in this situation. They've been charged with drink driving and the court hearing is around the corner. They often call us (and assume that we agree) that they have to plead guilty - "there's no other choice, is there?".

Not true. Every defendant has the right to plead not guilty to a drink driving charge. Please also remember that before the first court hearing we can obtain the initial evidence against you (known as the IDPC). If we can find any fault with the evidence against you, we may be able to persuade the police/CPS to drop the case before or during the first court hearing. Once we have the IDPC, we can then make clearer decisions regarding your plea and, of course, any available defences.

Next Steps

If you want more information about how to defend a drink driving case, you can review our Case Studies. Alternatively, please get in touch for free legal advice on 0151 422 8020.

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