One of Britain’s most senior civil servants, now embroiled in the Greensill scandal, breached government rules by failing to declare a trustee role he took up within a year of leaving office, the appointments watchdog has declared. Bill Crothers, who was the government’s chief commercial officer until 2015 and founded its £15bn-per-year business contracts division – the Crown Commercial Service – took the role with the UK’s purchasing and supply industry body in late 2016, without telling the watchdog. Crothers said he was not aware that the advisory committee on business appointments (Acoba) needed to be informed about unpaid roles, raising questions about how consistently rules were communicated throughout Whitehall. “I am afraid that when appointed, I did not think that Acoba approval was required due to it being a not for profit charity and an unpaid trustee role,” Crothers said, in a letter informing Acoba of the breach. “I am sorry for this honest mistake.” Acoba’s chairman, Lord Pickles, wrote to the Cabinet Office minister, Michael Gove, on Thursday to inform him that Crothers’ failure to declare his trusteeship with the Chartered Institute of Procurement & Supply (CIPS) breached government rules. “Failure to seek advice is a breach of the government’s rules and the requirement set out in the civil service management code,” Pickles said. “It is the committee’s policy to act transparently, including making public any failure to follow the rules that is it made aware of. It is now a matter for you to decide what appropriate action to take.” A Cabinet Office spokesperson said: “We have received the letter and will be considering its contents.” The former civil servant joined CIPS in November 2016, a year after he left Whitehall. He left the trustee position in December 2018. Crothers informed Acoba of his failure to declare the role in a letter on Thursday, as he contested suggestions that he had misled the committee when it was asked to issue advice on plans to launch his independent consultancy firm nearly a year after it was incorporated. Crothers is among a growing cast of former and current Whitehall officials embroiled in the Greensill Capital lobbying scandal. It emerged on Tuesday he started advising the now-collapsed lender Greensill two months before he left the civil service in November 2015. The decision to start advising Greensill, which netted Crothers a stake worth an estimated $8m (£5.8m) by 2019, was approved by the Cabinet Office. Company records show the ex-civil servant, who was paid up to £149,000 a year before leaving office, also incorporated his own firm in September 2015, at the same time that he began working for Greensill Capital as an adviser to its board. But Acoba has confirmed it only received the application to review Crothers’ consultancy work in October 2016, more than a year after the company was formed. The letter said Crothers was seeking advice on plans to “establish” the consultancy. However, company records show it already had £29,099 in the bank, was owed £31,500, and had debts of about £20,109 by September that year. It suggests the company was already established and operating. Crothers named his consultancy “Commercial Common Sense” after one of his catchphrases at the Crown Commercial Service – and mirroring its acronym. Crothers did not comment when approached by the Guardian. However, in a letter written to, and released by, Acoba on Thursday, in the wake of the Guardian’s queries, Crothers said all the business conducted over that year was linked to invoiced work that had already been approved. Crothers said it was a “misunderstanding” that he was requesting approval to “establish” and independent consultancy. “I had not requested, or intended to request, such approval,” he said. “Commercial Common Sense Limited was purely a vehicle for me to invoice my advisory work, consistent with your approvals, before Commercial Common Sense’s first year ended.” Acoba’s correspondence dating back to 2016 said Crothers planned to take contract work with Francis Maude Associates (FMA), led by Cameron’s former trade minister and Cabinet Office minister, Lord Maude of Horsham. This was described as Crothers’ “first commission”, which involved advising overseas government on how to improve the way they bought products, services and managed commercial contracts. The assignment meant working with the government in Australia, the ultimate headquarters of his other commercial interest, Greensill Capital. The Guardian has asked Crothers to confirm whether he held any other appointments that were not reviewed by Acoba during this time. Former ministers and senior civil servants are expected to report any new roles taken within two years of leaving office to their former departments, and the information is passed on to Acoba to review. Acoba gives advice on how to avoid conflicts of interest based on the government’s wider business appointment rules, but those are not legally binding. It does not have the power to block appointments.