A senior civil servant was granted permission to join the lender Greensill Capital while still working at the highest levels of government, a watchdog has revealed. Bill Crothers was head of Whitehall procurement, in control of a £15 billion annual purchasing budget, when he took on an external role as part-time adviser to the finance company's board in September 2015. Boris Johnson was understood to be personally concerned about the disclosure on Tuesday night, while Labour described it as "extraordinary and shocking", renewing demands for an MP-led inquiry into the lobbying row engulfing Greensill and David Cameron. The lender, which filed for insolvency last month, has been at the centre of controversy over the access its founder Lex Greensill was granted to numerous Whitehall departments during Mr Cameron's administration. The former prime minister then went on to join Greensill in 2018, and has been revealed to have directly lobbied Rishi Sunak and a series of other ministers on the company's behalf. Correspondence published on Tuesday between the appointments watchdog and the Cabinet Office revealed the overlap in Mr Crothers working for both the government and Greensill. Read more: The David Cameron/Greensill scandal explained In a letter to Lord Pickles, chairman of the Advisory Committee on Business Appointments (Acoba), Mr Crothers said of his role at Greensill: "It was seen as a way of me transitioning back into the private sector, and was supported by the Cabinet Office leadership." Suggesting other top mandarins had also taken on dual roles in the private sector, he added: "This advisory role was not seen as contentious, and I believe not uncommon." Mr Crothers then left the civil service in November 2015 and went on to become a director at Greensill the following year.