Just nine drug driving arrests were made by West Yorkshire Police in the first nine weeks of a new law to help police catch “high” motorists.

Figures obtained by the Institute of Advanced Motorists (IAM) reveal that nine motorists were arrested for driving under the influence of prescribed and illegal drugs between March 2 and April 29.

By comparison South Yorkshire Police made 55 arrests for the same offence in the same period while Greater Manchester Police made 26 arrests between March 2 and May 11.

Northumbria Police recorded the highest number of arrests with 97 between March 2 and April 30.

At the other end of the scale, Leicestershire Police, Warwickshire Police and Gwent Police made no arrests for the offence.

Insp Joanne Field, who leads West Yorkshire Police’s Roads Policing Unit, welcomed the new legislation.

She said: ‘‘The change in law, with set limits for both illegal and some powerful legal drugs, makes the process of tackling those who put lives at risk by drug-driving simpler by enabling us to test for the two most common illegal drugs at the roadside.

‘‘The influence that drugs, both illegal and medication prescribed by a doctor, can significantly impair someone’s ability to drive and put your life as well as those of other road users in significant danger just like drink-driving.

‘‘Cannabis and cocaine are the most common illegal drugs used by people who drug-drive and this new legislation increases our ability to identify and arrest people who drive with illegal drugs in their system.

‘‘Because the new law also sets limits for types of legal drugs it’s vital that anyone taking prescribed medication reads the instructions carefully and sticks to the prescribed dosage. If you have any concerns regarding the impact any medication may have on your ability to drive, please speak to your doctor before you get behind the wheel.

‘‘A drug-driving conviction will result in a criminal record, a minimum 12 month driving ban, a fine of up to £5,000 and up to 6 months in prison or both. It’s not worth the risk.’’

IAM chief executive Sarah Sillars warned that the figures did not mean certain forces were failing to make drug driving arrests.

Ms Sillars said: “I am sure the majority of law abiding drivers would like to know why there is such a variation in the data we have received from police forces. It would be unfortunate if some people got the idea that some areas are softer on drug-driving than others.”