Peter Mandelson has waded into the Labour leadership contest by criticising Ed Miliband for producing a "crowd-pleasing Guardianista" general election manifesto that was ignored by most voters.

In his most direct attack on the younger Miliband brother, the former business secretary mocked him for distancing himself from a work he produced.

"Nobody else authored the manifesto," Mandelson told Radio 4. "It was done by Gordon and Ed."

The ex-business secretary said the manifesto was designed to appeal to readers of the Guardian and "offered nothing to people worried about immigration, housing and welfare scroungers".

He described the document as "a lowest common denominator manifesto, a crowd-pleasing Guardianista manifesto that completely passed by that vast swath of the population who weren't natural Labour voters".

The remarks by Mandelson – who last month warned that Ed Miliband would lead Labour up an "electoral cul-de-sac" – reflect the views of Tony Blair, who believes the shadow energy and climate change secretary has no instinctive feel for middle England.

Blair is reported to have remarked that Ed Miliband would be a "disaster" for Labour.

Mandelson and Blair believe he wants to resort to the Labour "comfort zone" on the left by reaching out to the 1.5 million people who have switched to the Liberal Democrats since 1997.

Supporters of Ed Miliband dismissed Mandelson's remarks, saying he was in no position to criticise the manifesto because he ran Labour's election.

An Ed Miliband campaign source said he wanted to "make a clean break from the Blair, Brown, Mandy era because he recognises the scale of change we need to undertake in order to win again".

"Peter Mandelson, who is supporting David Miliband, grossly underestimates the scale of what needs to be done," the source said. "He is wrong if he thinks it is all down to the manifesto."

Labour party members have two days left to vote in the leadership contest before the ballot closes on Wednesday evening. The winner will be announced on the eve of the Labour conference on Saturday.