Drink driving is one of the most serious offences a motorist can commit and despite the common assumption that there is a standard 12 month disqualification, sentencing for this offence can be much more varied and severe.

Sentencing for drink driving is dependent on a number of factors however the first thing that the court would usually look at is the alcohol level in the sample taken by the police. Anybody charged with this offence will have provided the police with a sample of either breath Test, blood Test or urine test and each type of sample has its own set limit set out in the Road Traffic Act 1988 which are as follows:

  • 35 microgrammes of alcohol in 100ml of breath
  • 80 mg of alcohol in 100ml of blood
  • 107 mg of alcohol in 100ml of urine

When Is It Not Safe For Me to Drive?

Now that you know the legal limits it is important to know how much alcohol would equate to these levels of alcohol in your system; i.e how much can you drink before driving?

This is a difficult question to answer as each individual person will have different personal limits depending on how their body processes and metabolises alcohol. Factors that can impact this include (but are not limited to) a person’s height, weight, age and sex.

There are many sites online that are in place to try and help you know your limit such as on AlcoholConcern.org.uk however these sites do not employ an exact science and should never be totally relied upon when deciding if you are under the limit. They are helpful in providing a guide to how many units are in your favourite drinks!

On average, a pint of lager could contain 2 units of alcohol which would equate to 20µg of alcohol which is well on the way to the prescribed limit. 2 pints contains enough alcohol to put you above the limit with 40µg of alcohol however the body goes through an absorption and elimination period when drinking alcohol so the period of time over which drinks are consumed is relevant.

The safest way to ensure you do not drive whilst over the limit is to leave the car at home when you know you are consuming alcohol or, if in a group, arrange a designated driver.

Drug Driving Limits

Historically, motorists who were driving whilst impaired by drugs would face a charge of driving whilst unfit under Section 4 of the Road Traffic Act 1988 which carries similar penalties to those of drink driving. This often proved problematic for the Crown Prosecution Service however as they had to prove that a driver was not only impaired, but also that this impairment was caused by the presence of drugs (or alcohol depending on the charge). There was never any set limit for drugs the way there has always been with alcohol cases so securing a prosecution often proved difficult.

To combat this and in an effort to clamp down on driving whilst impaired through drugs, a new “drug driving” provision came into force on 02 March 2015. These new rules mean it will be an offence to be over the specified limits for a range of drugs whilst driving in a similar way to drink driving. The new legislation means that the prosecution will no longer have to prove that driving was impaired as it is now an offence to be driving whilst over the prescribed limit.

Following extensive consultations with medical experts, the limits included in the new regulations are not set at zero as drugs taken for some medical conditions can be absorbed into the body to produce trace effects.

So what drugs are included and what are the prescribed limits? The drugs are broken down into illegal drugs and those used for medicinal purposes.

‘Illegal’ drugs (‘accidental exposure’ – zero tolerance approach) Threshold limit in blood (per litre)
Benzoylecgonine 50µg/L
Cocaine 10µg/L
Delta-9-tetrahydrocannibinol (cannabis) 2µg/L
Ketamine 20µg/L
Lysergic acid diethylamide 1µg/L
Methylamphetamine 10µg/L
MDMA 10µg/L
6-monoacetylmorphine (heroin) 5µg/L


‘Medicinal’ drugs (risk based approach) Threshold limit in blood (per litre)
Amphetamine 250µg/L
Clonazepam 50µg/L
Diazepam 550µg/L
Flunitrazepam 300µg/L
Lorazepam 100µg/L
Methadone 500µg/L
Morphine 80µg/L
Oxazepam 300µg/L
Temazepam 1,000µg/L

You should continue taking any medicine(s) that have been prescribed to you as advised by your doctor or healthcare professional, or according to the patient information leaflet that comes with the medicine.

Unlike the old “impairment” law, this new legislation provides a medical defence if you’re taking your medicine in accordance with a instructions, provided that you are not impaired.


Drink Driving Limits