The founder of Greensill Capital - the firm which ex-prime minister David Cameron lobbied for - has denied his previous government role allowed him to win contracts for his business.
In a marathon three-hour evidence session to a House of Commons committee, Lex Greensill faced an array of questions related to the collapse of his finance firm in March, as well as his relationship with Mr Cameron.
He denied MPs' suggestions he could be viewed as a "fraudster" or that his business model of supply chain finance was a "Ponzi scheme" like that of infamous swindler Bernie Madoff.
Mr Greensill's business activities and Mr Cameron's lobbying of government ministers for access to government-backed COVID support schemes for Greensill Capital are currently subject to a string of inquiries at Westminster.
The Financial Conduct Authority (FCA) is also conducting a formal investigation, including over allegations about the firm's collapse - of which some "are potentially criminal in nature".
Continuing its own inquiry, the Commons' Treasury Committee on Tuesday grilled the Australian financier about his links to Mr Cameron - both while and after the ex-premier was in office.
Mr Greensill told MPs he was brought into the Cabinet Office as an adviser - when Mr Cameron was prime minister - during the "wreckage post the financial crisis".
He said he had been tasked with giving advice on how to "enable government to make interventions that helped small businesses to get cheaper access to credit or better access to credit".
"That was the reason I was brought in and I provided those services to the government at no cost," he added.
"I was simply trying to share my experience and give something back."
The Australian financier denied he would have been able to use his Cabinet Office role to boost his own commercial interests.
"Absolutely not," he said. "The first government-related business that Greensill Capital ever won and funded against was in July 2018.
"Greensill Capital didn't have any customers here in the UK until 2015."
In July 2018, Greensill Capital took over the supply chain finance scheme for NHS pharmacies.
Mr Greensill was quizzed about recent newspaper reporting on how a document advocating a supply chain finance scheme for NHS pharmacies ended up in Mr Cameron's red box while he was prime minister.
"It would not have been possible that a report that I could have written could have ended up in the prime minister's box," Mr Greensill replied.
He added: "It would simply be impossible for an adviser to write a report that ended up in the prime minister's box unless it had been reviewed by others."
Asked if a report could have been put into Mr Cameron's red box by then cabinet secretary Jeremy Heywood - who was a former colleague of Mr Greensill's at Morgan Stanley - Mr Greensill replied: "I can't speculate to that. But I guess that's possible, he was the cabinet secretary."
He added: "I wrote a number of papers that, it's my belief, ended up in the prime minister's red box and the pharmacies scheme was a scheme that was announced by the prime minister at the round table that was held, I think it was in October 2012."
Mr Greensill went on to employ Mr Cameron as an adviser to Greensill Capital in August 2018, once the ex-prime minister had left Downing Street.
Mr Cameron's numerous texts and emails to government ministers, officials and the Bank of England during the COVID crisis have been published by the Treasury Committee.
The ex-prime minister was said by Mr Greensill to have advised him "with respect to the growth of our business", as well as providing "analysis and geopolitical thinking".
Mr Greensill confirmed Mr Cameron was employed by his firm on a PAYE basis and had share options in the business.
He also told MPs how he and Mr Cameron travelled together on the company's private jets on occasion.
Despite Mr Cameron's lobbying efforts, Greensill Capital was declined access to the government's COVID Corporate Financing Facility last year.
However, the firm was approved to be eligible for a separate Coronavirus Large Business Interruption Loan Scheme by the government-backed British Business Bank.
During the evidence session, Mr Greensill said the collapse of his finance firm had caused "no loss" to the taxpayer.
He also apologised and said he took "complete responsibility" for the collapse of Greensill Capital.
"I am desperately saddened that more than 1,000 very hard working people have lost their jobs at Greensill," he told MPs.
"Likewise I take full responsibility for any hardship being felt by our clients and their suppliers, and indeed investors in our programmes."
Mr Greensill blamed his company's collapse on being "let down" by its principal insurer, adding: "To all of those affected by this: I am truly sorry."
But Labour MP Rushanari Ali likened Greensill Capital's business model to "a Ponzi scheme".
"Frankly, it smacks of fraudulent behaviour and it smacks of the sort of stuff we saw conducted by the likes of Madoff in the financial crisis," she said.
Mr Greensill admitted to a "flaw" in his business but described supply chain finance as "the future".
Meanwhile, fellow committee member and Labour MP Siobhain McDonagh asked Mr Greensill if he was "a fraudster".
"No, Ms McDonagh, I'm not," he replied.
Mr Cameron is due to make his own appearance before the Treasury Committee on Thursday.