Bickering to the end, battle of the Milibands goes down to the wire

Friends of David accuse rival of bid to influence betting market

Tension between David and Ed Miliband reached a new height last night as they waited anxiously to find out which of them will be elected leader of the Labour Party today.

Bookmakers, who had made David the front-runner since the race began in May, suddenly installed Ed as the favourite yesterday just as the votes were being counted.

Friends of David accused their opposite numbers of moving the betting market by making false claims that the two Miliband camps had held talks on how to handle a result that would leave one brother a triumphant winner and the other a deeply disappointed loser.

"They are trying to portray David as contemplating defeat; he is not," said one ally of the shadow Foreign Secretary. "He has stuck to his guns and his values in this campaign and not told the party what it wanted to hear. If the party wants a different direction, so be it. He can hold his head high."

A former Cabinet minister who is backing David conceded there were last-minute jitters that he would be pipped at the post by his younger brother. "The party may vote with its heart rather than its head," he said.

Supporters of Ed, who is politically to the left of David, suggested bookmakers had finally caught up with the momentum that would take him over the finishing line. They hinted at informal discussions on how to handle the result, despite a strong denial from David's team.

The Ed Miliband camp gave off the air of confidence. His partner Justine Thornton, who is expecting their second child, will travel to Manchester for the result, then head back to London, and has made plans to return to the conference on Tuesday when the new leader will make his all-important keynote speech.

The Milibands and the three other candidates – Ed Balls, Andy Burnham and Diane Abbott – will not know the result until about 3.58pm today. They will be in separate side rooms with one aide, and will have to surrender their phones and Blackberries so that they cannot communicate with the outside world. They will be called to a central room and told the result.

Their body language will be studied closely as they walk on to the conference platform at 4pm. Ed Miliband will be accompanied by his campaign agent Sadiq Khan, the shadow Transport Secretary, and David by his political adviser Madlin Sadler.

There are not meant to be any coded signals to supporters and broadcasters, which can go wrong. In the 2007 deputy leadership contest, Gerry Sutcliffe, agent to the favourite Alan Johnson, was supposed to take off his glasses if his man had won. He was so surprised by Harriet Harman's victory that he forgot and put his head in his hands. Ms Harman's close allies knew she had won – because, by prior arrangement, she had her handbag over her left shoulder.

Gordon Brown and Ms Harman, the acting leader, will make speeches before the result is officially announced by Ray Collins, the party's general secretary, and Ann Black, the chairman of Labour's national executive committee.

The announcement, due at 4.30pm, is unlikely to be short and sweet. No one is expected to win more than 50 per cent of first preference votes, so the one coming last will drop out and the second preferences of the people who backed him or her will be redistributed until one candidate wins a majority. These votes will be crucial. It is impossible to predict how they will split. But some Labour MPs believe Ed Miliband's campaign has been tailored towards winning them.

After the result, the contenders will put on a show of unity under the new leader. It won't be easy for the Milibands to rebuild a relationship that has soured during the election.

While the loser contemplates his future, the winner will have to prepare quickly for his first major interview as leader – on the BBC's Andrew Marr Show tomorrow.