One of the UK’s biggest trade unions, Unite, has cut ties with a key supplier and opened an independent inquiry over concerns about financial irregularities. An assistant general secretary of the union told employees it was suspending ties with the company “primarily due to the risk of committing an offence under the Proceeds of Crime Act 2002”. A spokesperson for the company involved confirmed that it had “assisted the police with certain investigations” but said it categorically denied any wrongdoing, adding: “No charges of any nature have been brought against any person in any way associated or connected with our company.” The Guardian is not naming the company for legal reasons. Unite cut ties with the company this month, and the accountancy firm Grant Thornton is carrying out an investigation, which is due to report next month. A Unite spokesperson said Sharon Graham, its general secretary, had commissioned the external forensic investigation into Unite’s affiliated service providers. “The general secretary is committed to ensuring that no stone is left unturned in uncovering the truth about these matters and taking whatever steps are necessary to protect our members’ interests,” the spokesperson said. “In this regard, the union recently severed its relationship” with a supplier. “It should be made clear that the union is sharing and will continue to share any pertinent information we obtain about these matters with the police and other relevant authorities.” It comes after 20 officers from South Wales police raided the office of a Unite employee in London in April and took away material as part of their inquiries. At the time, a police spokesperson said: “South Wales police has executed warrants as part of an investigation into allegations of bribery, fraud and money laundering. The warrants were executed on Wednesday 6 April at addresses in the South Wales, Metropolitan, Merseyside, Cheshire, North Wales, Dyfed Powys and Northamptonshire police force areas. “The joint investigation with Her Majesty’s Revenue and Customs is continuing and a number of suspects will be interviewed in due course.” Graham was elected as general secretary of Unite last year on a platform of change, while planning to cut donations to Labour and divert the money to union campaigns. Separately, she ordered an inquiry into the soaring costs of construction of a Birmingham hotel and conference centre, which is alleged to involve a loss of about £70m. This is also due to report in December and is being conducted by a KC, whom the Guardian understands to be Martin Bowdery. The initial projected cost for the 170-room complex was £57m, but the cost rose to £98m, an increase that Unite said was a result of safeguarding employment practices onsite. The Guardian was leaked documents in January 2021 showing that the costs of the controversial building project had increased by millions.