The former Foreign Secretary David Miliband has said he is "optimistic" about the prospect of Andy Burnham becoming the next prime minister.

Miliband told a think tank event in London on Friday that Burnham, who is widely expected to succeed Sir Keir Starmer as Labour leader and prime minister, has "this openness and energy that I think is very attractive and positive".

He said the expected appointment of the former Labour cabinet minister James Purnell as Burnham's Downing Street chief of staff was "fantastic".

"I haven't lost my youthful optimism," Miliband told an event organised by the Center for Global Development think tank.

"Andy Burnham, James [Purnell] and I came into the House of Commons at the same time in 2001 and I think [Burnham has] always had this remarkable ability to listen, to connect, to process data and ideas and information."

There has been speculation Miliband, the older brother of Energy Secretary Ed Miliband, could return to front-line politics in a Burnham government.

He quit as MP for South Shields in 2023 to take up the posts of president and CEO of the International Rescue Committee (IRC) - jobs he still holds.

Usually a prime minister's cabinet is made up of MPs from the House of Commons.

But in theory, Miliband could join the cabinet if he is given a peerage in the House of Lords, as former Prime Minister David Cameron was when he became foreign secretary in Rishi Sunak's Conservative government.

Burnham has mainly talked about domestic policy since he won the Makerfield by-election and is due to give a speech about the economy and devolution on Monday.

At the event, the BBC asked Miliband what his message to the next prime minister was about UK spending on aid, and whether he was interested in joining Burnham's government if he entered Downing Street.

Miliband said: "My message is of course to read the IRC's publications because they provide such an evidence-based and innovative and cost-effective way of serving the most vulnerable and poverty-stricken parts of the world. So there you go."

When asked later whether he had been in contact with team Burnham recently, he did not reply.

Someone who knows Miliband told the BBC he would be "a massive asset to Andy Burnham's cabinet," citing his work on the international stage in foreign affairs, humanitarian action and climate change.