A national poster campaign will feature close-up images of the Prime Minister grinning, alongside negative claims about his record in office.

Slogans featured next to Mr Brown's profile included "I took billions from pensions - vote for me" and "I let 80,000 criminals out early - vote for me".

The poster were released as the war of words between Labour and the Conservatives intensified with less than six weeks to go until the expected May 6 election. Polls this weekend continued to point to a hung parliament, with the Tories' lead still short of what Conservative leader David Cameron needs to be sure of a Commons majority.

Created by M&C Saatchi - the architects of the successful "Labour isn't working" campaign in 1979 - the posters marked a toughening of the Tories' positioning.

Previous posters have featured a similarly close-up shot of Mr Cameron, which was accused of being air-brushed by Labour and has been savagely spoofed on the internet.

The new focus on Mr Brown indicates Tory confidence that the premier is a potential liability for Labour. The posters will be displayed on 850 poster sites in England and Wales from Monday.

The Tory leader admitted the election would be a "close fight" but insisted it was one the Conservatives had to win for the good of the country.

Mr Brown acknowledged Labour was "the underdog", but insisted the party would "never give up". He said: "We are fighting for Britain's future - and we intend to win."

He set out Labour's five key pledges for the election, which he said were "substantial, deliverable and carefully costed". They were to secure the recovery, raise family living standards, build a "high tech" economy, protect frontline investment in policing, schools, childcare and the NHS, and strengthen fairness in communities.