A top civil servant was approved to take a job working for the bank at the centre of the David Cameron lobbying row while still working for the government.
Bill Crothers, the Government’s former Head of Procurement, became an adviser to Greensill Capital while he was a civil servant, newly published letters reveal.
The Cabinet Office gave him permission to take the job in September 2015, two months before he left his role in Government.
Mr Cameron joined Greensill later, in August 2018 - two years after he stepped down as Prime Minister.
Because Mr Crothers was already working for the firm before leaving, the Cabinet Office decided Mr Crothers would not have to apply to Whitehall's "revolving door" regulator, the Advisory Committee on Business Appointments (ACOBA).
Following an inquiry from ACOBA chair Lord Pickles, the Cabinet Office replied: "Mr Crothers took up a role advising the Board of Greensill Capital in September 2015 whilst he was employed as a Civil Servant.
"This was agreed via the Cabinet Office internal conflicts of interest policy, which advises on how to address real or perceived conflicts of interest."
They added: "Mr. Crothers then left the Cabinet Office and the Civil Service, at the end of November 2015. As he was already working in an advisory capacity to Greensill before he left the Civil Service, with this role captured under the conflicts of interest policy, no BAR application was required to be submitted to ACOBA at this time."
Labour will tomorrow try to pile pressure on Boris Johnson over the row - forcing a Commons vote on the affair.
MPs blasted Boris Johnson's plan for a "whitewash" No10 review of the scandal, saying the government can't be trusted to "mark its own homework."
The opposition will force a vote to establish a committee-style probe with the power to ask witnesses - including Mr Cameron, the Chancellor and other ministers - to give evidence.
Boris Johnson today insisted a review of the scandal, to be led by senior Lawyer Nigel Boardman, would have the "maximum possible access".
He said Mr Boardman had been given “pretty much carte blanche to ask anybody whatever he needs to find out.”
The Prime Minister added: “I would like it to be done quickly, but I want him to have the maximum possible access so we can all understand exactly what has happened, and that will of course be presented to Parliament in due course."
But speaking in a Commons debate in response to an Urgent Question on the affair, Labour's Jon Trickett told MPs: "It sounds like a whitewash to me."
The PM's review will look into how he failed bank was given access to a Covid loan scheme for businesses - which put hundreds of millions of pounds in taxpayers' money at risk.
The firm later collapsed into administration but not before former prime minister David Cameron unsuccessfully lobbied ministers on its behalf in a bid to ask for Treasury support for the bank.
Labour want to see a new Commons select committee created to investigate lobbying, including Mr Cameron’s activities in support of the collapsed lender.
If MPs back the idea, a cross-party committee would investigate whether current laws are enough to prevent "inappropriate lobbying" of ministers and officials.
Deputy Labour leader Angela Rayner said: "The Tories can't be trusted to mark their own homework after handing billions in taxpayers' money to their donors, mates and cronies."
Mr Cameron sent a number of texts to Chancellor Rishi Sunak's private phone when bidding for Government support for Greensill.
It was later reported that the former Tory leader had arranged a "private drink" between Health Secretary Matt Hancock and Australian financier Lex Greensill to discuss a payment scheme later rolled out in the NHS.
Mr Hancock admitted to MPs he "attended a social meeting" organised by his former boss that he had "reported to officials in the normal way".
Mr Cameron also emailed a senior Downing Street adviser, pressing for a rethink on Mr Greensill's application for access to emergency funding.
The former PM finally broke his silence at the weekend with a statement in which he insisted he had not broken any rules, but accepted there were "lessons to be learned".
In the Commons, Business Minister Paul Scully argued the Chancellor had provided a "comprehensive response" to questioning on the Greensill matter.
He said: "The Government recognises the interest in the matter and it is right that we now let that investigation, that review happen and do its work.
"But in line with the approach and the interest of transparency, as I say, the Chancellor has provided all of the message(s) that were sent from him to David Cameron on this matter and they relate exclusively to Greensill's proposals for the Covid Corporate Finance Facility."