The former Prime Minister appeared before Parliament’s Treasury Committee today and claimed he had “no sense at all” that the company was in danger.
Mr Cameron sent ministers and officials 45 emails, texts and WhatsApp messages relating to the now-collapsed firm in less than four months.
The bankruptcy forced the owner of Liberty Steel, which employs about 5,000 people, to seek a bailout.
Speaking virtually, Mr Cameron insisted there was “absolutely no wrongdoing” in his actions but admitted former prime ministers “need to think differently and act differently”.
He said: “I was paid an annual amount, a generous annual amount, far more than what I earned as prime minister, and I had shares – not share options but shares in the business – which vested over the period of time of my contract.
“I had a big economic investment in the future of Greensill, so I wanted the business to succeed, I wanted it to grow.
“The fact that I have this economic interest, that’s important, but I don’t think the amount is particularly germane to answering those questions, and as far as I’m concerned it’s a private matter.”
Mr Cameron repeatedly refuse to say exactly how much money he made, but labelled suggestions he was to make £60 million “completely absurd”.
He also refused to tell the committee chairman whether his salary was higher or lower than £1 million.
Mr Cameron added: “It was a generous, big salary that you might earn as someone in my position at a bank or what have you.”
Labour MP Angela Eagle claimed Mr Cameron’s behaviour was “more like stalking than lobbying”.
She said: “I read your 56 messages and they’re more like stalking than lobbying – looking back are you at least a little bit embarrassed about the way you behaved?”
Mr Cameron replied: “The Government was introducing plans to try and help businesses, we thought we had a good idea.
“I was keen to get it in front of Government, but as I’ve said, there are lessons to learn, and lessons for me to learn, and in future the single formal email or formal letter would be appropriate.”
Ms Eagle also confronted the former Prime Minister on how many times he used one of Greensill’s private jets to fly to or from Newquay, close to his third home, or any other non-business declarations.
He answered: “I haven’t got a complete record of the use of the planes.
“It was used quite a lot by Lex Greensill and senior managers, and sometimes myself on business visits.
“I did use it a handful of times on other visits, and of course all proper taxes and all those things would be dealt with in the proper way.”
Mr Cameron also insisted he was not offered a job while prime minister by Lex Greensill, who was advising the Government at the time.
He added: “I think I met him twice while I was in Downing Street and I can absolutely confirm at no stage did he ever suggest that I would go and work with him or for him afterwards.
“That happened after I left office.”