At least a million people go to work with drugs in their system, a study suggests.
Around one in 30 employees tested at work last year had taken narcotics, with the most prevalent drugs being cannabis, opiates and cocaine, figures from drug testing firm Concateno showed.
Drug use among employees was also up 43% from 2007, rising to 3.23% last year from 2.26%.
The figures come from an analysis of 1.7 million tests carried out for 856 UK employers, including public transport firms, freight haulage and the emergency services.
Dr Claire George, Concateno's laboratory director, said: "These are conservative figures when you consider how many companies do not have a screening programme in place.
"Concateno has seen an increase in the number of businesses seeking assistance with drug and alcohol screening programmes, in order to identify, deter and reduce the risks associated with drug use in the workplace."
The report also found the most likely age group to test positive for Class A drugs were 25 to 34-year-olds - not the under-25s - as they were likely to have more access to disposable income.