Former prime minister David Cameron will be questioned by MPs later over his work lobbying for collapsed finance firm Greensill Capital.
His unsuccessful attempts to obtain access to government-backed loans for the company during the pandemic have led to scrutiny of lobbying practices.
The government has said Greensill's applications were dealt with properly and were ultimately rejected.
In an earlier statement Mr Cameron insisted he had not broken any rules.
But he acknowledged he should have used "only the most formal of channels".
Mr Cameron, who has not yet spoken publicly about his actions, will appear before both 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 on behalf of Greensill, including sending nine WhatsApp messages to Chancellor Rishi Sunak and 12 texts to Sir Tom Scholar, the permanent secretary of the Treasury.
Greensill had hoped to take part in a government scheme - the Covid Corporate Financing Facility (CCFF) - set up to help businesses during the pandemic.
However, the Treasury rejected its application, concluding the firm's proposals were not suitable.
Reports of Mr Cameron's lobbying led Boris Johnson to order a review by lawyer Nigel Boardman into decisions made in government around the finance scheme and the role of Lex Greensill, founder of the company.
Earlier this week Mr Greensill said he took "full responsibility" for the firm's collapse when he appeared before the Treasury Committee.
The Financial Conduct Authority has also launched an investigation into the failure of Greensill, which filed for insolvency in March, and said "potentially criminal" allegations had been made about its circumstances.