Cameron, who was prime minister from 2010 to 2016, appointed the Australian banker as an adviser when he was in Downing Street. After leaving office, Cameron in turn became an adviser to Greensill's now-insolvent finance firm.

Cameron has faced criticism for contacting ministers directly on behalf of Greensill Capital, which recently collapsed.

The Financial Times and Sunday Times newspapers have reported that Cameron sent texts to UK finance minister Rishi Sunak and arranged a private drink between Greensill and health minister Matt Hancock.

Britain's Treasury has said that the former prime minister contacted Sunak and two other ministers in the department to ask if Greensill could access the government's COVID-19 loan schemes.

In his first comments on the row, Cameron said that in his representations to government he was breaking no codes of conduct and no government rules.

Ultimately the outcome of the discussions on Greensill's proposals regarding the loan were not taken up, he said, and therefore his interventions did not lead to a change in the government's approach.

"However, I have reflected on this at length," he said in a statement to the Press Association news agency.

"There are important lessons to be learnt. As a former Prime Minister, I accept that communications with government need to be done through only the most formal of channels, so there can be no room for misinterpretation."

The collapse of Greensill Capital has put thousands of jobs at risk in the UK and Australia, including at the Whyalla Steelworks in South Australia.

Australian Associated Press