The British foreign secretary said the 2013 vote against intervention had limited the U.K.'s ability to influence events in Syria.
Blair's shadow may hang over the party but challengers to Corbyn should still look to his example to win.
The Times newspaper has reported that Miliband told friends he'd be taking a step back.
Final opinion polls showed Prime Minister David Cameron's Conservatives and Ed Miliband's opposition Labour Party almost in a dead heat.
Two polls on the final day of campaigning found Labour and the Conservatives tied
Cameron's "Little England" policies do not augur well for a U.S. foreign policy which encourages like-minded states to share the burdens of leadership.
Labour deal with SNP would result in "mayhem" says former Conservative PM as knife-edge election race continues.
Labour leader polls 35% after debating four smaller party leaders, including SNP's Nicola Sturgeon, who got 31%.
The opposition leader's closest aide, Lord Wood, says the Conservatives have become the "nasty party" again.
Prominent tax expert counters Tory claims that scrapping of non-dom status would cost Britain money.
Vote on EU membership would create "most intense period of business anxiety" since WW2, Blair said.
Opinion polls after the event all produced different winners.
The contest comes before an unusually close national election on May 7.
Bubbling under the UK's general election campaign is a promised referendum on EU membership. Is Britain heading for the way out?
Britain's continued membership of the European Union hangs on the outcome of the election on May 7.
Miliband said he is a "resilient guy" and believes he has been underestimated.
Cameron gave an interview on Monday in which he said he wouldn't seek a third term as prime minister.
In a heated exchange, Ed Miliband said David Cameron was making "pathetic, feeble excuses".
David Cameron reiterated his refusal to attend the debates, despite broadcasters saying they would go ahead without him.
Alan Johnson also said that Ed Miliband should articulate the need for greater economic equality in Britain.
The Conservative party held a fundraiser this week where some tickets cost more than a minimum wage salary.
A new model predicting the outcome of the election produced a 94.5% chance of a coalition government.
The Times/YouGov poll shows the Scottish National Party would take 48% of the vote to Labour's 27%.