The far-right British National Party won its first seat in the European Parliament yesterday, a breakthrough that will add to pressure on Prime Minister Gordon Brown.
The BNP gained the seat in the northern English region of Yorkshire and Humber at the expense of Brown's Labour Party, which has been hurt by a scandal over politicians' expenses and questions over Brown's leadership.
Labour also lost a seat in Wales, a traditional stronghold, where its share of the vote slumped 12 points to 20 percent and it was beaten into second place by the centre-right Conservatives.
Losing a seat to the BNP will give fresh ammunition to Brown's critics in the Labour Party after a traumatic week in which six senior ministers quit the government, one of whom called on Brown to quit and said he was an electoral liability.
Rebels among Labour members of parliament (MPs) are said to be canvassing support for a letter calling on Brown to stand down to boost their chances at a general election due within a year.
The Conservatives have a commanding lead over Labour in opinion polls and are on course to return to power for the first time since 1997.
Critics say the party lacks a coherent policy agenda and that Brown is indecisive, a poor communicator and unable to transfer his confidence on the world economic stage to domestic politics.
Labour members of parliament are due to meet on Monday when rebels could go public with their criticisms of the leader.
A change of Labour leader would raise the prospect of a snap election. Brown has not faced the electorate since he took over as prime minister from Tony Blair two years ago.
Last week, sterling was hit by speculation over Brown's future, and if he manages to survive the current crisis, it looks likely he will wait for as long as possible before calling the next election, due within a year.
Brown, who reshuffled his government team on Friday after the resignations, told supporters on Sunday he would not walk away from the country's troubles.
At a Labour event in London, staged to show Brown still had support among grassroot party activists at the end of a tumultuous week, he set out his policies on public services for the coming weeks and months.
He said the country had been through a "testing time" politically and economically, but added: "What would they (the public) think of us if ever we walked away from them at a time of need? We are sticking with them."
Brown is under pressure after a drubbing in Thursday's local election.
All the main parties have been tarnished by a scandal over expenses claims by MPs, but Labour is bearing the brunt of voter rage for having presided over the system.