Boris Johnson has promised a top lawyer will be given "carte blanche to ask anybody whatever he needs" as part of a review into the activities of a collapsed finance firm David Cameron lobbied for.
The prime minister has asked Nigel Boardman to look into the role of Australian financier Lex Greensill, his business, Greensill Capital, and its involvement with the government.
It follows weeks of allegations about the links between Mr Greensill, Mr Cameron and government ministers and officials.
Mr Cameron, who was employed by Mr Greensill in 2018 after he had left Downing Street, has been revealed to have approached serving ministers about the involvement of Greensill Capital in government-backed financial support schemes during the coronavirus crisis.
This included text messages sent to Chancellor Rishi Sunak.
Mr Cameron also had a drink with Health Secretary Matt Hancock, also attended by Mr Greensill, at which they are reported to have discussed a payment scheme later rolled out in the NHS.
After ordering the Greensill review, Mr Johnson said 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."
Pressed on why he had not set up a "full independent inquiry", the prime minister said he had "every confidence" in Mr Boardman, as he praised his "outstanding" work in previously reviewing government procurement processes.
And asked what he made of Mr Cameron’s lobbying on behalf of Greensill Capital, Mr Johnson replied: "That’s a matter for Nigel Boardman’s report."
"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," he added.
"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."
Mr Greensill was brought into government in 2011, when Mr Cameron was prime minister, to advise on supply chain finance.
Labour attempted to haul Mr Sunak before MPs on Tuesday to answer an urgent question about Greensill Capital’s access to the Coronavirus Large Business Interruption Loan Scheme (CLBILS).
But the chancellor did not appear in the House of Commons with business minister Paul Scully instead answering MPs’ questions.
Mr Scully said the scheme was the responsibility of the Department for Business, Energy & Industrial Strategy (BEIS) and not Mr Sunak’s Treasury.
But Labour’s shadow chancellor Anneliese Dodds highlighted how Mr Sunak previously "took the credit" for CLBILS and "personally announced those schemes".
She accused Mr Sunak of "running scared" from the Greensill scandal, adding: "It was the chancellor who needed to come to the House today.
"The chancellor who told David Cameron he would push his team to amend emergency loan schemes to suit Cameron’s new employer.
"The chancellor whose officials met with Greensill 10 times."
Mr Scully said Mr Sunak had already provided a "comprehensive response" to Ms Dodds over her questions about Greensill.
Downing Street said Mr Boardman’s review into Greensill Capital "won’t have legal powers", but said it will "have access to all the necessary information required".
Mr Boardman will pause his work as a non-executive director of the Department for Business, Energy & Industrial Strategy while the review is carried out.
A spokesman for Mr Cameron said: "We welcome this inquiry and will be glad to take part."