Gordon Brown was heading for another mauling in the polls tonight as the first results in the European elections showed a sharp fall in the Labour vote.
With Mr Brown's political survival hanging in the balance, deputy leader Harriet Harman admitted that they were expecting a "very dismal" night.
In Labour's North East heartland - the first region to declare - the party saw its share of the vote drop 9% since the last elections in 2004.
Ms Harman told the BBC: "We are bracing ourselves for very dismal results, there is no doubt about that."
Worryingly for Labour, the UK Independence Party (Ukip) and the far right British National Party both made advances, with their share of the vote increasing by around 3% each.
If Ukip manage to beat Labour into third place or the BNP make a breakthrough and gain their first European seat, it would intensify the pressure on Mr Brown from rebel Labour backbenchers pressing for a leadership challenge.
Ms Harman sought to deflect attention from the Prime Minister, putting the blame for Labour's poor performance on the row over MPs' expenses which, she said, had hit the party particularly hard.
"Our supporters are absolutely furious with us about expenses," she said. "They expect us to have higher standards than the Tories."
Labour Chief Whip Nick Brown challenged Labour rebels weighing the prospects for a leadership challenge to either make their move or rally behind the Prime Minister.
"The time has come for them to nominate their candidate, see if they've got sufficient nominations and take the issue to a party conference," he told the BBC.
"If they can't do that, they should get behind the leadership that the overwhelming majority of party members support."