Video report by ITV News Political Correspondent Carl Dinnen
Boris Johnson has said a review into how failed firm Greensill Capital was able to secure Government contracts will be given the "maximum possible access" to get to the bottom of what happened.
Downing Street announced on Monday that senior lawyer, Nigel Boardman, has been commissioned to carry out a probe into how the specialist bank - founded by Australian financier Lex Greensill - was granted access to a Covid loan scheme for businesses, putting hundreds of millions of pounds 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 support for Greensill through the Government's Covid Corporate Financing Facility (CCFF).
The prime minister told broadcasters on Tuesday: "I've asked Nigel Boardman to have a look at this whole issue of supply chain finance and given him pretty much carte blanche to ask anybody whatever he needs to find out.
"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."
Mr Johnson said it was for Mr Boardman to judge on his predecessor's behaviour.
Mr Cameron sent a number of texts to Mr Sunak's private phone when bidding for CCFF support for Greensill.
It was later reported that the former Conservative Party leader had arranged a "private drink" between Health Secretary Matt Hancock and Mr 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".
Matt Hancock on his involvement in the Greensill scandal:
Mr Cameron also emailed a senior Downing Street adviser, pressing for a rethink on Mr Greensill's application for access to emergency funding.
Mr Johnson was pressed on whether he was looking to "rough up a rival" via the review given the long history between him and Mr Cameron.
The Prime Minister replied: "I think people have got questions that they need to satisfy themselves about - including me - about how this supply chain finance stuff is meant to work.
"I don't think it is going on at present anywhere in Government, but we need to understand exactly what the intention was, how it came about, and that is exactly what Nigel Boardman is going to do."
Shadow chancellor Anneliese Dodds was granted an urgent Commons question calling on Chancellor Rishi Sunak to explain his involvement with the Greensill affair.
But the Government argued that the wording of Labour's urgent question meant it should instead be dealt with by junior business minister Paul Scully because officials said Greensill was chosen as a lender by the British Business Bank, which is separate from the Treasury.
Ms Dodds accused Mr Sunak of "running scared" from the Greensill scandal and highlighted the number of times the Treasury had taken credit for the Coronavirus Large Business Interruption Loan Scheme (CLBILS).
Later, Labour MP Toby Perkins described the lobbying affair as being "grubby" and "shabby".
But Mr Scully replied by arguing that the Chancellor had provided a "comprehensive response" to questioning on the Greensill matter.
He told the Commons: "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."
The issue is set to be revisited by MPs on Wednesday when Labour will push to a vote a plan to establish a parliamentary inquiry into Mr Cameron's lobbying activities.
Labour want to see a new Commons select committee created to investigate lobbying, including the former prime minister's activities in support of the collapsed lender.
If MPs approve the motion, the cross-party committee would investigate whether current laws are sufficient to prevent "inappropriate lobbying" of ministers and officials.