It also emerged that the UK lacks national guidelines for drugs-testing because the organisations which might have created them have been privatised, meaning that their views do not carry any official weight with private companies. Instead, standards set by the US government are used, in a haphazard fashion.
Dr Alexander Forrest, of the Royal Hallamshire Hospital in Sheffield, said that the lack of clear legislation in the UK could lead to abuse by employers during random testing of employees or job applicants for use of drugs such as heroin, cannabis, cocaine and alcohol.
"If workplace drug-screening is regarded by the employer as a non-medical issue, then the employee should have the same protection as ... in a criminal investigation," writes Dr Forrest in the Journal of Medical Ethics, published today. "Such protection may require new legislation."
His comments echo those of Dr John Honour, who in yesterday's Independent said: "There aren't any standards for positive tests or for how the tests should be done ... If you failed a pre-employment test you might not even hear - you'd just not get offered the job."
Dr Honour's knowledge of urine-testing and pharmacology helped clear the name of Diane Modahl, the athlete wrongly suspended in 1994 for taking drugs. But he is concerned that although drugs-testing is growing rapidly, there are no national standards.
A major testing laboratory yesterday told The Independent that the only standards currently used by drugs-testing laboratories are those set by the US National Institutes for Drug Abuse (NIDA).
The UK does not have any of its own because the only government organisations which might have set them - the National Physical Laboratory and the Laboratory of the Government Chemist (LGC) - have been privatised.
Most companies use some form of the NIDA standards. But those are far from perfect.
"Basically, when these were introduced in the 1980s in the US, they set them as low as their testing equipment could manage," said Mr Walker.
However, that is sometimes too sensitive. Laboratories are aware that their tests can give a positive result for opiates if someone eats a bagel covered with poppy seeds.Reuse content