Labour MPs in marginal seats called on Gordon Brown last night to change the law to stop the Conservatives from pumping money into target constituencies before the next election.

Mr Brown, addressing a lengthy meeting of the Parliamentary Labour Party at Westminster, tried to assure his MPs that he could strengthen their defence of marginal seats with more help in direct mailing and internet campaigning.

But a series of MPs with small majorities urged him to go further, arguing that Lord Ashcroft, the Conservative party deputy chairman who is pouring money into marginal-seat campaigning, was exploiting a legal “loophole” that Mr Brown should close.

The demand was led by Martin Linton, MP for Battersea, who began the questions after Mr Brown made a 20-minute speech arguing that he had smoked out some of David Cameron’s policies. Mr Linton’s call for a change in the law was followed by similar questions from other MPs in marginal seats, including David Borrow, Stephen Ladyman and Celia Barlow.

Mr Brown told them that he would consider their points but did not give a specific pledge. Year-round limits to election spending, rather than local spending limits once a campaign begins, are being considered in cross-party talks on party funding but progress has stalled over Labour’s financial links with unions.

Some MPs told Mr Brown that they had not wanted an election, which they said would have been unnecessary. One backbencher said later: “There was some navel-gazing about how we got into the mess in the first place.”

A Labour official admitted that there had been some criticism of the handling of the election announcement. Michael Connarty, a left-wing MP, told Mr Brown that he thought the perception of the way things were handled was a shame and unnecessary. But Labour sources said that there was no outright criticism after a Brownite loyalist, Nigel Griffiths, told MPs not to make public criticisms of Mr Brown but keep comments within the PLP.

Mr Brown told the MPs that the threat of an early election had forced Mr Cameron to reveal the outline of his manifesto and said it gave Labour the chance to repeat its campaign strategy of 2001 and 2005 by attacking the Tories’ tax plans as a threat to the economy and public services.

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