Random checks suggest that around 6% of workers could be under the influence of drugs and alcohol.

Heathrow Terminal 5 client BAA has stepped up drug testing on the flagship site after random checks suggested many of the sites workers could be under the influence of drugs and alcohol.

It emerged this week that a series of random tests, carried out on groups of around 60 workers at a time, consistently showed around 6% tested positive for alcohol and drugs including cannabis and cocaine. The figure raises concerns that more of the project's 8600 workers could be operating under the influence of drugs and alcohol.

BAA has now introduced monthly random tests in a bid to curb drug and alcohol use on the site. A spokesperson confirmed: "To ensure that Terminal 5 remains drug and alcohol free, the number of random tests undertaken was recently increased. The results of these tests are in alignment with previous figures, with a minor percentage testing positive."

Workers who fail tests are immediately suspended from working on the site. Employers are then responsible for investigating the incident and initiating disciplinary procedures.

Although the level of drugs and alcohol use amongst workers on the project has fallen since the project began due to a sustained health and safety campaign by BAA, and remains relatively low compared to police estimates of the use in the locality as a whole, drugs and alcohol use remains a large concern for the industry. Wembley contractor Multiplex recently sought police advice after allegations that dozens of the 3500 workers on the project were working under the influence of cannabis and cocaine.