The man behind Greensill Capital - Lex Greensill - worked as an unpaid adviser to David 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 company.
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. He pressed Treasury ministers - including sending Chancellor Rishi Sunak text messages - for emergency funding for the company, in which the former prime minister had a financial interest. David Cameron and Lex Greensill also met Health Secretary Matt Hancock for a "private drink" in 2019 to discuss a new payment scheme for NHS staff.
Mr Cameron is reported to have told friends he was set to earn as much as £60m from shares in Greensill, where he had worked since 2018.
In the end, Mr Cameron's pleas to the Treasury for emergency loans for Greensill Capital were not successful. The firm has now gone bust, throwing the future of thousands of workers at Liberty Steel, a company backed by the finance firm, into doubt.
Mr Cameron didn't appear to do anything wrong, under the current rules. He stood down as prime minister in July 2016 and joined Greensill in August 2018.
Although Mr Cameron has been cleared by a watchdog of breaking lobbying registration rules, a Sunday Times investigation has shed new light on his dealings with Mr Greensill when he was prime minister, in the early days of the Conservative/Lib Dem coalition.
In 2012, Mr Greensill was made an unpaid adviser in Mr Cameron's government, with a Westminster pass and access to government departments. He used this access to promote a government-backed loan scheme he had devised. Mr Greensill stood to make a lot of money from the scheme. He helped to convince the UK government to set up a supply chain finance scheme for pharmacies - paying them early for money they were owed by the NHS. In 2018, Greensill Capital won the contract to run it.
Questions had been asked before about the sustainability of Greensill's business since at least 2018. But the final blow came last July, when one of its insurance companies withdrew cover that protected some of Greensill's investors.
The relationship between those at the top of government and big business has never been under more scrutiny, following questions over the way Covid contracts were awarded. Critics argue that it is too easy for ministers and top civil servants to use their inside knowledge of Westminster to enrich themselves when they leave government.
There is also a question of access. There are thousands of lobbyists - from trade unions to environmental groups to multinational companies - why do some people appear to get favoured treatment?
The government says the review, which will report back by to PM Boris Johnson by the end of June, will examine the awarding of contracts for supply chain finance. Downing Street says it will look at "how contracts were secured and how business representatives engaged with government".