JCB, one of the UK’s biggest manufacturers, is investigating a spate of drug use among workers based at its headquarters and has sacked a “significant” number of staff, the Guardian can reveal. A message sent to UK employees last week by the digger-maker’s group human resources director, Max Jeffery, seen by the Guardian, said it had been conducting a “series of investigations into substance misuse” over the past two months. This had resulted in a “small but significant number of people leaving JCB”. The message, entitled “Substance Misuse and Workplace Safety”, said investigations continued. Sniffer dogs have been used by private security at turnstiles at its Staffordshire headquarters, on production lines and in offices at the site last week. JCB, via its lawyers Schillings, said 22 staff tested positive for drugs or alcohol or refused to take a drugs test after being detected by sniffer dogs deployed at its sites over the course of a week. Of the 22 workers, it said about 75% tested positive for cannabis via urine testing, and further laboratory tests were being carried out on the results. JCB said the staff did not hold senior management positions. It did not say whether other drugs, including class A drugs such as cocaine that sources claim have been used by workers, were found in any tests. It said a further 11 UK workers had been sacked or resigned between April and December after refusing to take part in routine drug and alcohol testing or testing positive. JCB claimed it had the “inverse” of a drugs problem, that no drugs had been found on its sites, and said it had a “zero-tolerance approach to drug use and alcohol abuse”. There have been concerns about staff taking drugs on site and investigations have resulted in workers being pulled off production lines, sources allege. JCB’s lawyers said thorough and ongoing investigations at the company had found no evidence of drugs being taken or stored on site. JCB’s lawyers said it was “technically accurate to say that our client has not pro-actively informed the police (because their thorough investigation has not found evidence of illegal drugs on any JCB site)”. They added that officers were “aware of the situation” after a local newspaper informed police about sniffer dogs at the site. JCB’s lawyers claimed it was a relatively small number of workers who had tested positive, compared with estimates of drug use by the wider UK population. They argued that this meant the company had the “inverse” of a drugs problem. The JCB group of companies employs 8,000 people in the UK across its factories in Staffordshire, Derbyshire and Wrexham, and about 15,000 people in total worldwide. The drug use findings and wider allegations pose a headache for the company, which is owned by the Bamford family, who have been big donors to the Conservative party. Workers in the automotive and other manufacturing industries are often subjected to random drugs tests given the dangerous nature of their work and the potential implications for the safety and reliability of the equipment they make. After questions from the Guardian, JCB’s lawyers said on Tuesday that it investigated allegations that managers had been supplied with drugs in October, and the company was shown alleged screenshots of messages dating to July 2023 that appeared to show three employees buying and using drugs. It said JCB’s “reasonable conclusion” was that these were likely to be “prescription-based drugs” and the veracity of the screenshots was “never fully substantiated”. The company said individuals named in the messages tested negative for drugs. JCB is one of the world’s biggest makers of agricultural and construction machinery. It exports about 75% of its UK total production, generating export revenues of about £1.35bn, according to the company’s website. Anthony Bamford, the company’s Brexit-backing chair, has been among the most significant donors to the Conservative party in recent decades. He holds directorships for a wide range of JCB group companies. The company was founded by his father, Joseph Cyril Bamford, in 1945. The Tory peer has also bankrolled the lifestyle of the former prime minister Boris Johnson, paying for and hosting Johnson’s most recent wedding at the Bamford family’s Daylesford estate. He also funded the Vote Leave campaign to quit the EU. In October, the Guardian revealed that Lord Bamford and his brother Mark’s financial affairs were under investigation by HMRC.