Workplace drug testing has increased significantly across the UK, according to four drug screening companies, reports the BBC. Over the past four years the four companies have reported increases of between +40% to +470% in the number of tests they have carried out.

Under current UK law, employees must consent to drug testing. Government policy currently dictates that employers should limit testing to employees that need to be tested, ensure that the tests are random, and do not single out particular employees for testing unless this is justified by the nature of their jobs.

Workers cannot be forced to comply with drug tests, but if they refuse when the employer has good grounds for testing, they could face disciplinary action.

Speaking to the BBC, Lianne Gray, Strategic Account Manager for LGC Group, one of the testing companies, said that employees in safety-critical roles; such as those operating heavy machinery or driving, and government agencies were most likely to be screened.

There is a growing trend, however, for drug screening to be conducted in “more normalised industries”, such as healthcare and retail, as businesses look to “safeguard not only the business, but also the reputation in the field they work in.”

Ms Gray said: "Traditionally we see requests for amphetamines, cocaine, cannabis, opiates. Now we're seeing more requests for things like ketamine, steroids, and also for novel psychoactive substances - or legal highs as they're otherwise known." 

The increases in drug testing have angered civil liberties groups, who say that the practice is an invasion of people's privacy outside of safety critical roles.

Niamh Eastwood from the drugs advice charity, Release, said they frequently took calls from people who had falsely tested positive for drugs. Eating poppy seed bread, for example, can indicate the presence of opiates in some tests.

She said another problem is that although drug tests may indicate what substances are in the system, they do not indicate how, and if, a worker's performance is likely to be affected.

Fiona Coombe, Director of Legal and Regulatory Research at Staffing Industry Analysts also advised caution on the part of employers. “Drug testing should be consented to by employees and workers, with such consent being obtained in the employment contract or in staff handbook policies before the employment starts. However it still needs to be reasonable in the circumstances, and unless it can be justified employers run the risk of discrimination and unfair dismissal claims. There may also be issues relating to data protection and privacy.”