Re: They don't rely on drug tests for past use
DV clearance in the UK tends to be far more encompassing than just ‘Top Secret’. If you are likely to come into contact with any form of sensitive data or be working within a ‘knife-throw’ of any MP then you can often expect to be subject to microscopic checks. Unfortunately it can take many months to complete, which used to mean for me that a contractor had been vetted and completed the contract months before security rejected him/her as ‘failed’.