How the police test for drug driving

The Department for Transport has released figures from the Cheshire constabulary showing a 800% increase in arrests for drug driving.

The increased number of arrests is largely owing to the widespread use of so-called drugaliser devices which can detect drugs in a person’s system within as little as 8 minutes by analysing saliva. Previously, this preliminary indication was not available.

Under the old legislation, which is still in force today, a person would have to perform a series of impairment tests and would usually only be brought to the police station and face a blood test if they failed the impairment test .

The use of the drugaliser device is resulting in far more people being brought into custody following the identification of drugs in their system at the roadside.

On the 28th February 2016, the government announced that police forces have been given an additional £1 million to train officers, purchase drug screening equipment and pay for samples to be analysed

How does the roadside drug test work?

  • The drugaliser device works by analysing the driver’s saliva for the presence of drugs.
  • The device is placed into the driver’s mouth to obtain saliva cells.
  • The police officer then waits for the result.
  • The result will appear within 8 minutes.
  • If the device identifies drugs in the driver’s saliva then a positive result will appear as a line on the device, similar to a pregnancy test.
  • The roadside drug swabs can only currently test for cocaine and cannabis.

How are drugs other than cocaine and cannabis detected?

Until more comprehensive roadside testing devices are granted “type approval”, the police must rely on impairment tests to detect the possible presence of drugs other than cocaine and cannabis in a person’s system at the roadside. These tests include:

  • The Romberg test: which tests balance and judgement
  • The walk and turn test
  • The standing on one leg test
  • The finger to nose test
  • The pupil measure test: assessing the size of the pupils

Targeted approach to identifying drug drivers

The police are using a targeted approach based on statistics which show that young male drivers are more likely to drug drive.

To mark the one year anniversary of the new drug driving law coming into force, the government has launched an advertising campaign aimed at young male drivers.

If a police officer thinks that a driver is under the influence of drugs, they can ask them to take a roadside drugs test.  Alternatively, they can ask the driver to perform a police impairment test.

Failing or refusing the test will result in the person being arrested and taken to the police station where they will be asked to provide a blood test.   The driver would be prosecuted on the basis of a positive blood test rather than the preliminary indication provided by the roadside drugs test.

What are the drug driving limits and how long do drugs stay in your system?

Click here to view the drug driving limits.

Article written by expert drug driving solicitor, Alison Ashworth; Managing Director of Ashworth Motoring Law.

Alison Ashworth; Expert motoring lawyer and Director of

Ashworth Motoring Law are experts in defending drug driving offences. In fact, we have a 100% acquittal rate in defending drug driving offences. If you have been arrested for drug driving and would like specialist advice and representation by a drug driving expert, contact our free motoring law advice line on 0330 33 22 770 or email

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