Drug driving charge from prior cannabis use

This depends heavily on the context in which the test is carried out. The legal and practical consequences vary significantly depending on whether this is a roadside drug test, a workplace drug test, or something else entirely.

Driving and roadside drug testing:

Under the Drug Driving (Specified Limits) (England and Wales) Regulations 2014 and section 5A of the Road Traffic Act 1988, it is an offence to drive with certain controlled drugs in your blood above specified limits. For delta-9-tetrahydrocannabinol (THC, the active component of cannabis), the limit is 2 micrograms per litre of blood. This is an extremely low threshold, deliberately set near zero.

The offence is strict in the sense that the prosecution does not need to prove you were impaired. It only needs to show the substance was present in your blood above the specified limit. The fact that you consumed cannabis days earlier is not a defence. If THC remains in your system above that limit at the time you were driving, the offence is made out.

THC can remain detectable in blood for varying periods depending on frequency of use, body composition, metabolism, and the amount consumed. For regular users, it can remain above the legal limit for days after consumption.

The consequences of a conviction for drug driving are serious. These include a minimum 12 month driving disqualification, an unlimited fine, up to 6 months imprisonment, and a criminal record. The conviction will also show on your driving licence for 11 years, and it is likely to substantially increase your motor insurance costs.

Workplace drug testing:

The position here depends on the terms of your employment contract, your employer's drug and alcohol policy, and the nature of your role. Many employers, particularly in safety-critical industries such as transport, construction, and the military, carry out random or for-cause drug testing. A positive test for cannabis metabolites, even if use occurred days before, can result in disciplinary action up to and including dismissal.

Whether a dismissal in these circumstances would be fair depends on factors including the clarity and communication of the policy, the nature of the role, whether the policy was applied consistently, and whether a reasonable investigation and disciplinary process was followed. For safety-critical roles, tribunals have generally accepted that a zero tolerance policy, strictly applied, can support a fair dismissal even where there was no impairment at work.

Cannabis is a Class B controlled drug under the Misuse of Drugs Act 1971, so possession and use remain criminal offences in England and Wales regardless of the testing context.

If you can tell me the specific context in which you are facing or anticipating a drug test, I can give you much more targeted guidance on your options and any possible defences or mitigation.