Financier Lex Greensill worked as an unpaid adviser to Mr Cameron when he was prime minister, and developed a policy designed to ensure small firms got their bills paid faster. The scheme also benefited Mr Greensill's own company, Greensill Capital.
Mr Cameron went on to work for Greensill Capital after leaving office, and tried unsuccessfully to lobby the government to increase the firm's access to government-backed loans.
Mr Cameron pressed Treasury officials - including reportedly sending Chancellor Rishi Sunak text messages - for emergency funding for Greensill Capital, a company in which the former prime minister had a financial interest.
Mr Cameron is reported to have told friends he was set to earn as much as £60m from shareholdings in Greensill, where he had worked since 2018.