David Cameron is to face a grilling by MPs over his lobbying activities for collapsed finance firm Greensill Capital.

The former prime minister is appearing at back-to-back hearings by the Commons Treasury and Public Accounts committees.

On Tuesday, the Treasury Committee released dozens of texts and emails Mr Cameron sent to ministers and senior officials appealing for their help in gaining access for Greensill to Government Covid support programmes.

They included messages to Chancellor Rishi Sunak and Cabinet Office minister Michael Gove, and senior officials at the Treasury and the Bank of England, as well as a call to Health Secretary Matt Hancock.

Mr Cameron has insisted his lobbying activities, after joining the firm as an adviser after he left office, broke no rules, although he has accepted there are “lessons to be learned”.

The Government has also said Greensill’s applications were dealt with properly and were ultimately rejected.

However there has been criticism of how a former prime minister was able to exploit his personal contacts with former colleagues and officials in the pursuit of commercial gain.

In one message to Mr Sunak, Mr Cameron complained the Treasury’s objections to Greensill’s application were “nuts”, adding: “Think there is a simple misunderstanding that I can explain.”

In an exchange with Mr Gove, the former prime minister messaged: “Am now speaking to Rishi first thing tomorrow. If I am still stuck, can I call you then?”

“Of course! Any time,” Mr Gove responded.

Meanwhile the City watchdog has said it is launching a formal investigation into the collapse of Greensill which filed for insolvency in March.

The Financial Conduct Authority said some of the allegations made about the firm were “potentially criminal in nature”.

Greensill was the biggest backer of GFG – the owner the UK’s third largest steelmaker, Liberty Steel – and its failure has put thousands of jobs at risk as GFG seeks to refinance.

Appearing before the Treasury Committee on Tuesday, the firm’s founder, Australian financier Lex Greensill, said he was “truly sorry” and took full responsibility for what happened.

In a letter to the committee, Mr Cameron said he first became concerned that the company might be in serious financial difficulty in December last year.

“Up until that point, I firmly believed that Greensill was in good financial health,” he said.