David Miliband has delivered a scathing critique of Labour under his brother's leadership, dismissing it as backward-looking and out of touch.

The former foreign secretary gave his frankest response yet to the devastating election defeat as the party's MPs started to nominate potential successors to Ed Miliband.

Frontrunners Andy Burnham, Yvette Cooper and Liz Kendall have already achieved the 35 backers required to make the final ballot. Left-winger Jeremy Corbyn - with 11 - and shadow international development secretary Mary Creagh - with five - still have work to do before nominations close on June 15.

Mr Burnham, Ms Cooper and Ms Kendall were jeered by union activists at a GMB hustings yesterday after they refused to condemn Tory plans to reduce the benefit cap to £23,000.

In an interview with CNN, Mr Miliband - who moved to New York to run the International Rescue Committee charity after narrowly losing the 2010 leadership contest to Ed - was asked how Labour could recover from its grim results.

"I think what is important for all the candidates is to reflect on the very clear lessons of two devastating electoral defeats of the Labour Party in the last five years which have come for a very clear reason," he said.

"And the reason is that the public have concluded that instead of building on the strengths and remedying the weaknesses of the Blair years the party has turned the page backwards rather than turning the page forward.

"So I think it is the responsibility of all the candidates to find again that combination of economic dynamism and social justice that defined the success of the Labour Party in the 1990s and early 2000s."

Mr Miliband pointed out that Labour was still in power in many of the country's northern cities.

"Those local government leaders are making their voice heard to a national party that needs to catch up with the way Britain has changed, the way politics has changed and the kind of agenda that needs to be set in an age of economic insecurity which is what exists across Europe at the moment," he said.

In an interview with The Times, Mr Miliband said his "worst fears were con-firmed" when the results started to come in on May 7.

He said the party's pitch had made him "very fearful of the consequences", and he felt "frustration and anger" about what a Conservative majority govern-ment would mean for Britain.

The defeat was was "doubly painful" because of his brother's involvement. "I don't want him to be hurt and I don't want him to be vilified," he said. "There is no consolation in any sense of vindication, frankly, because I care about the country and I care about the party."