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Driving under the influence of alcohol or drugs

Drink driving

The legal alcohol limit in England, Wales and Northern Ireland for driving is 80 milligrams of alcohol per 100 millilitres of blood or 35 micrograms of alcohol per 100 millilitres of breath. In Scotland the limit is 50 milligrams of alcohol per 100 millilitres of blood or 22 micrograms of alcohol in 100 millilitres of breath. There is no way to know how much you can drink and stay under the limit, since it can depend on your weight, age, metabolism, the amount of food you've eaten and other factors. It's impossible to get alcohol out of your system quickly, it always takes time. A shower, a cup of coffee or other ways of ‘sobering up’ may make you feel better but won’t remove the alcohol from your system. If you've been out drinking, you may still be affected by alcohol the next day and could lose your licence if you drive and are still over the legal limit. Alcohol affects everyone differently and any amount can impair your ability to drive. The only safe option is to avoid alcohol completely if you’re driving as even ‘just one drink’ could put you over the limit. If you’re driving, don’t drink any alcohol at all. Drug driving It's an offence to drive with any of 17 controlled drugs above a specified level in your blood. This includes illegal and legally prescribed drugs. The limit set for each drug is different, and for illegal drugs the limits set are extremely low. They aren't zero to rule out any accidental exposure (eg from passive smoking). You should always check with your doctor or pharmacist if you're unsure about whether your prescription or over-the-counter medication will affect your ability to drive.

Risks and physical effects

The biggest risk you take when driving under the influence of alcohol or drugs is the risk of causing a collision. Driving under the influence of drink or drugs is extremely dangerous and can affect your driving in numerous ways, such as:

  • ability to judge speed and distance

  • reaction and coordination skills

  • blurry or impaired vision

  • drowsiness

  • aggression

  • erratic behaviour

  • panic attacks and paranoia

  • hallucinations

  • nausea

  • dizziness

  • tremors

Alcohol and drugs can also create a false confidence which can lead to an increase in risk-taking behaviour, which puts your life and the lives of others in danger. Testing for alcohol and drug use


The police can stop you at any time and ask you to take a breath test (‘breathalyse’ you) if:

  • they think you’ve been drinking

  • you’ve committed a traffic offence

  • you’ve been involved in a road traffic collision

If you refuse to take a breath test, or fail to supply a sample of breath and don't have a ‘reasonable excuse’, you can be arrested. A reasonable excuse could be a genuine physical or mental condition stopping you from giving a sample; in this case you may be required to have a blood test. The breath test gives a result straight away. If it shows you’re not over the drink drive limit, you may be allowed to go. If you fail the breath test, you’ll be taken to a police station and given a final breath test. If it’s positive, you'll be charged.


The police can stop you and conduct a roadside screening test or a field impairment test, both of which may result in your arrest if:

  • they think you have taken drugs

  • you’ve committed a traffic offence

  • you’ve been involved in a road traffic collision

Officers can test for cannabis and cocaine at the roadside, and screen for other drugs – including ecstasy, LSD, ketamine and heroin – at a police station. Even if you pass the roadside check you may still be arrested if the police suspect that your driving is impaired by drugs and you can be taken to a police station for further tests.


If you're found to be over the drink-drive limit, and/or driving while impaired by drugs, you can receive:

  • a criminal record

  • a maximum penalty of six months in prison

  • an unlimited fine

  • an automatic driving ban of at least one year (three years if you have been convicted twice in 10 years)

Other problems you may face include:

  • an endorsement on your driving licence for 11 years

  • an increased insurance premium

  • if you drive for work, your employer will see your conviction on your licence

  • trouble travelling to countries like the USA

Penalties for causing death whilst driving dangerously under the influence of alcohol or drugs If a driver kills someone while under the influence of alcohol, they can be charged with causing death by careless driving while under the influence of drink or drugs (Section 3A of the Road Traffic Act 1988 (as amended by the Road Traffic Act 1991, section 3)). The maximum penalty is 14 years imprisonment if the offence was committed before 28 June 2022. If the offence was committed on or after 28 June 2022, the maximum penalty is life imprisonment.

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