image copyrightPA Mediaimage captionDavid Cameron stepped down as PM after the Brexit referendum in 2016
The Treasury has released text messages sent by Rishi Sunak to David Cameron, amid an ongoing row over lobbying.
Mr Cameron sent messages to the chancellor's private phone last year to ask for help for finance firm Greensill Capital.
The former PM was working as an adviser to Greensill. The two replies show Mr Sunak told Mr Cameron his suggestion was not possible.
Mr Cameron's messages to Mr Sunak have not been released.
In a document detailing the messages, officials said Mr Cameron had sent the messages as a Greensill employee with an expectation that they would remain confidential.
A source close to Mr Sunak said Mr Cameron had messaged the chancellor "multiple times" on his personal phone.
The source added he had chosen to publish the messages "in order to reassure beyond doubt that there was no wrongdoing and that he acted with integrity and propriety".
In a reply on 3 April 2020, Mr Sunak told Mr Cameron: "Hi David, thanks for your message. I am stuck back to back on calls but will try you later this evening and if gets too late, first thing tomorrow. Best, Rishi".
In the second reply on 23 April, Mr Sunak said: "Hi David, apologies for the delay. I think the proposals in the end did require a change to the Market Notice but I have pushed the team to explore an alternative with the Bank that might work. No guarantees, but the Bank are currently looking at it and Charles should be in touch. Best, Rishi"
It is understood that "Charles" refers to Charles Roxburgh, the second most senior civil servant at the Treasury.
The 23 April message relates to Greensill Capital's desire to be part of a government-backed Covid loan scheme. The "Bank" Mr Sunak refers to is understood to be the Bank of England, which was running the Corporate Covid Financing Facility, a scheme to help big firms through the crisis.
The Treasury said the firm's requests were eventually rejected by officials, although Mr Cameron reportedly went on to unsuccessfully lobby the government over a different scheme.
Labour's shadow chancellor Anneliese Dodds said: "There must be a full, transparent and thorough investigation into the chain of events that saw Greensill awarded lucrative contracts, the freedom of Whitehall and the right to lend millions of pounds of government-backed Covid loans."
The Treasury released the text messages after being inundated with Freedom of Information (FOI) requests relating to the Greensill row.
Mr Cameron was investigated last month by a lobbying watchdog, which looked at whether he should have declared himself on the register of consultant lobbyists over his work for Greensill.
The Registrar of Consultant Lobbyists concluded that his activities had not fallen within the criteria that required registration.
Lex Greensill, the Australian founder of Greensill Capital, has yet to comment on the row. The firm recently collapsed.
Mr Cameron has also declined requests for a comment.