David Cameron was today told his reputation was “in tatters” after a parliamentary committee heard that his campaign of messages and calls to ministers and officials was “more like stalking than lobbying”.

In what he admitted was “a painful day” for him, the former Conservative prime minister was subjected to two gruelling sessions of questioning over his role in collapsed finance firm Greensill Capital. One MP told him he had damaged democracy by allowing himself to be “used” by someone who was a “con-artist”.

Mr Cameron admitted receiving “a generous big salary”, well above his £150,000 pay as PM, as senior adviser to Greensill, as well as shares in the company.

But he refused under repeated questioning to name the figure, insisting it was “a private matter”. Suggestions he stood to gain £60m if the firm succeeded were “completely absurd”, he insisted.

Documents released earlier this week showed a barrage of messages to ministers, including chancellor Rishi Sunak, and officials at the Treasury, Bank of England and No 10 from March to April 2020 as he fought to get Greensill access to state coronavirus support schemes in the early months of the pandemic.

Mr Cameron told the House of Commons Treasury Committee that he now agrees he ought to have made formal approaches by letter, but insisted his use of private phone numbers of former colleagues was “acceptable” and that Whitehall civil servants had not been “intimidated” his contact.

He acknowledged that there was a case to tighten the law so that a company’s employee who lobbied ministers would have to register their contacts in the same way that lobbying agencies do.

He also said it might have been “beneficial” for him to receive advice on the propriety of his business interests after leaving No 10, admitting “ex-prime ministers are different”.

But committee member Dame Angela Eagle told him his pursuit of Mr Sunak, Treasury permanent secretary Tom Scholar and health secretary Matt Hancock was “more like stalking than lobbying”, asking him: “Looking back, aren’t you at least a little embarrassed by the way you behaved? … Don’t forget, there were thousands of people dying at the time.”

Another MP, Siobhain McDonagh, told him: “You had the enormous privilege of being the prime minister of our country … Do you not feel that you have demeaned yourself and your position by WhatsApping your way around Whitehall based on a fraudulent enterprise, based on selling high-risk debt to unsuspecting investors?”

Mr Cameron insisted that his motive for seeking access for Greensill to the government’s Covid Corporate Financing Facility was “to help UK firms at this moment of difficulty” by providing an effective means of getting them credit.

But committee member Rushanara Ali told him his access with the highest ranks of government “smacks of favouritism and power – those in power like yourself with powerful connections and relationships getting access to decision-makers, and having that access to the VIP lane, the fast lane into what you want”.

Ms Ali told Cameron his conduct was “fundamentally damaging to our democracy”, adding: “You are the architect of the Lobbying Act, you should have known better…

“In your own words, you were the future once. I have no pleasure seeing a former prime minister being used in this way by somebody who was frankly a con-artist.”

But Mr Cameron told Ms McDonagh: “My view is that what I did was I made a choice to work for a business which I hoped would be a UK FinTech success story – and many people believed that it would – and I wanted to help that company.

“What I did at that time of economic crisis was put to the government what I genuinely believed was a good idea of how to get money into the hands of small businesses and get their bills paid early.”

Despite founder Lex Greensill’s evidence earlier this week that he had informed Mr Cameron as early as March 2020 that the company was experiencing difficulties, the ex-PM insisted he did not believe it was at risk of failing at the time he was lobbying ministers.

Treasury committee chair Mel Stride told him: “Many people would conclude that, at the time of your lobbying, your opportunity to make a large amount of money was under threat. You really must have known that.”

But Mr Cameron responded: “I did not believe, in March or April, when I was doing this contact, that there was a risk of Greensill falling over.”

He added: “I absolutely had a big economic investment in the future of Greensill, I wanted the business to succeed, I wanted it to grow.”

Mr Cameron confirmed that he regularly attended Greensill board meetings, but said he was not a member and that it had been a “mistake” when he referred to Bill Crothers in a message as a “fellow director”.

He admitted using the Greensill private plane for personal use, but said he did not have “a complete record” of flights. He said he used the plane “sometimes on business visits” and a “handful of times” on other visits, but did not confirm whether he took it to Newquay, near to his holiday home in Cornwall.

He pledged to pay tax on any flights deemed to be a benefit in kind, telling MPs: “Everything I’ve done I’ve paid full UK tax on….I don’t have any money offshore.”

The former PM told the committee that he met Mr Greensill no more than twice while the financier was working in the Cabinet Office from 2012.

“I can confirm that at no stage did he suggest I could go and work with him or for him after I left office,” he said.

Greensill invited him to work as a senior advisor in 2018, two years after he left office, supplying geopolitical and strategic advice, helping with international expansion, speaking at customer and supplier events, and helping to win new customers. Lobbying was not part of his job until the Covid crisis struck, he said.

“I liked the fact that the business was using technology and deep capital markets to help small businesses and supply chains to get low cost credit,” he said.

He said that Greensill’s Earnd app, which was taken up by parts of the NHS after a private meeting with health secretary Matt Hancock, was designed to “stamp out the evils of payday lending” by allowing staff to get wages up-front through official channels rather than going to loan sharks.

Asked for his message to thousands of workers whose jobs are at risk at Liberty Steel, owned by major Greensill client Sanjeev Gupta, Mr Cameron said: “Obviously I am very keen for Britain to continue to have a steel industry… I hope those steel jobs can be maintained.”

He denied that Greensill’s failure had put Gupta’s GFG Allliance in jeopardy, adding: “It’s the symbiotic relationship that went wrong between the two.”

Challenged over the losses incurred by investors in Greensill – including a number of towns in Germany – Mr Cameron said: “If anyone does lose money through their investments, that’s a matter for regret.”

In a tweet, Labour deputy leader Angela Rayner said Mr Cameron’s defence was that he had acted “within the rules”.

She added: “That’s the problem, Dave. That’s why we need to scrap this broken system that does nothing to regulate the revolving door, dodgy lobbying and favours for mates.”