I don't like this bit from the Gov.uk website -

"If the police stop you and think you’re on drugs they can do a ‘field impairment assessment’. This is a series of tests, like asking you to walk in a straight line."

I can't walk in a straight line, stone cold sober, with or without my medication - but my wobbly walking doesn't affect my driving.

Without an equivalent to the breathalyser this new law will soon become ridiculed.

Edited by RT on 27/02/2015 at 20:55

The field impairment test is considerably more than just a straight line walk.

It has been used by UK police forces for some time now and is an indicator which will be used as the trigger for further tests eg blood analysis.

But anyone on prescribed medication will obviously have it show in a blood test - the law makes "Impairment To Drive" the offence, not the presence of a prescribed medication in the blood stream .

The police/prosecution should be required to prove impairment to drive, not impairment to walk in straight lines nor the expected presence of prescribed medication in the bloodstream.

As far as I have seen the drug detection system works as follows:-

Illegal drugs are tested on a zero tolerance basis - if you test postive for them you're arrested. The road -side test is some sort of saliva swab tester which if positive will result in a urine test at the police station.

The prescription drug levels are varied according to the drug, there are some details here:-

Nine prescription drugs so far have legal limits set per litre of blood. Those using them within recommended amounts will not be penalised.

These are:

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