But what of the legal implications? Should employers be responsible for what their staff do in their free time?
Dr Ian Oliver, chief constable of Grampian Police, which has begun random drug-testing among its 1,800 officers and civilian staff - the first force to do so - has no doubt about employers' responsibilities.
"No employer has the civil liberty to ignore the consequences of substance abuse in the work-place and the impact that has on the public," Dr Oliver says in People Management magazine. "Anyone who wants to argue on the contrary needs their head seeing to."
John Wadham, director of Liberty, sees matters differently. "As a general rule it is an issue of privacy and employers should not take on the role of policing their employees unless their behaviour or ability to do the job is affected," he says. "It is obviously sensible to have a drugs policy. Employers want to be able to deal with any difficulties in a sensitive way and there are certain safety-critical areas where you have to be more careful. But I am not sure I would say random testing is acceptable."
Studies suggest that about one in 20 employees is likely to be a drug- abuser, with a higher incidence among 17- to 29-year-olds. In the City, the percentage of people testing positive during pre-employment screening is said to be as high as 10 to 15 per cent, mostly for cannabis.
Many employers already make the possession, or being under the influence, of alcohol or drugs a serious disciplinary offence, generally subject to summary dismissal.
Ronnie Fox, employment law specialist and senior partner in the City law firm Fox Williams, says it recommends including the right to test and search employees at random in the terms and conditions of employment.
"But we also recommend that employers treat it as a welfare issue, allow time off for counselling sessions and show a caring attitude," he adds. "I have advised a firm of accountants, for example, on how to deal with a partner with a severe alcohol problem. You always have to consider not only the effect the course of conduct will have on the particular employee but also how his colleagues will perceive his treatment. If they see someone given the plastic bag treatment, they will hide any habit. If he is offered treatment, counselling or time-off it might encourage others to seek help before any problem gets out of control.
"Employers face a number of potential liabilities, including personal injury and constructive dismissal claims from employees harmed by someone who was under the influence of drugs or alcohol and personal injury claims from members of the public harmed by an employee under the general vicarious liability principle. They could also face criminal prosecution for breaching health and safety legislation and be charged if their policies were such that they facilitated the misuse of drugs."
Social and legal attitudes towards drugs and alcohol differ even though the biggest killers are all legal - tobacco, alcohol, solvents and paracetamol.
Mr Fox says industrial tribunals treat substance abuse as a health issue. "But they tend to be more strict about drugs than alcohol."
John McMullen, national head of employment law at Pinsent Curtis, says his firm has drawn up drugs and alcohol policies for about six large companies in recent months, mostly in the finance and information technology sector. "Clearly, if you wish to introduce a drugs policy covering existing employees, it will require a change of their terms and conditions of employment. It needs to be done sensitively if the policy includes testing because it is an invasion of privacy.
"Employees have a right to say no to those changes and enforcing them could be a breach of their contract. It is a grey area as employers have some freedom to manoeuvre in the exercise of their managerial prerogative. But the way to do it is to get the employees to buy into the corporate need for such a policy."
A case last year raised questions about pre-employment screening when a television executive sued the company doctor who had advised his prospective employers that his drinking habits barred him from a lucrative job. The High Court decided that the doctor had a duty of care to the job applicant but he had not been negligent.
The legal consequences of ignoring the issue are spelt out in a guide for employers called "Drugs in the Workplace", produced by Chief Inspector David Williams, of Greater Manchester Police's drug prevention unit. He says a survey of the top 100 employers in the North-west found nine out of 10 did not see drugs as a problem. Those that had policies took a punitive view - possession equals dismissal.
But he adds: "That is not the way to deal with it. From a policing perspective, for every employee sacked, there is the likelihood they might turn to crime. We want employers to take a more balanced response and take the drug out of the work-place, not the individual"nReuse content