Meanwhile, Prime Minister Gordon Brown continued his faltering campaign to be returned as the country's leader in the election on May 6, and voiced his determination to fight to the end.

"You will see us fighting every minute of every day, every second of every day, for every vote until the campaign is complete."

"I'm fighting not just for my life but I'm fighting for what I believe is important for the future of the country," he said. "I never give up and I will never give up."

Brown made his vow as he campaigned in the northeast of England, a region where Labor is a strong performer.

Brown's campaign took a heavy self-inflicted blow on Wednesday when he called a pensioner voter he had had a discussion with in front of the media a "bigot" because she raised the issue of immigration.

It became headline news and may yet be one of the defining moments of the campaign. Brown took another blow when he was ranked last out of the three main leaders in a live TV debate on the economy on Thursday.

He was further frustrated when he opened the nation's most prestigious paper The Times on Saturday morning to find that it had dumped its support of Brown and Labor and backed the Conservatives.

The Times is owned by media mogul Rupert Murdoch, and the move brings it into line with his other daily national newspaper The Sun, which ditched Labor a while ago in favor of the Conservatives.

The left-of-center Guardian had also withdrawn its support from Labor, and now backs the Liberal Democrats.

But there was some solace in the polls for Brown, with the above mentioned two polls showing that his party had moved out of third place and overtaken the Liberal Democrats for second spot.

Liberal Democrat leader Nick Clegg, the surprise star of the campaign and now a force in British politics in a way no leader of the third party has been for 90 years, called for change to the first-past-the-post electoral system.

"I think David Cameron has made a huge error in setting his face against changing politics in this country," he said.

"He really has revealed his true colors, which are, despite all the talk about new politics, he doesn't really want to change very much at all."

Clegg said he thought the breakthrough his party had achieved in the opinion polls on the back of his star turn in the first live TV debate had unleashed an unstoppable move for reform. "You can't put the genie back in the bottle, I don't think you can turn the clock back," he added.