The reasons why Gordon Brown blinked and abandoned plans for an autumn general election lie in 50 marginal seats where Tory candidates are said to be in an unprecedented state of readiness.

Had Mr Brown pressed the button for a snap poll, Conservatives in these key battlegrounds were ready for a 72-hour campaign blitz bankrolled by the party’s £2 million “field operations” fund. But it was not just the prospect of well-funded local Tory campaigns in a three-week election that stayed Mr Brown’s hand; for months, Tory candidates in such seats have laid the groundwork, directed by Lord Ashcroft, the deputy party chairman.

A poll of 83 marginal seats yesterday found the Conservatives ahead of Labour by 6 per cent. The News of the World/ICM survey put the Tories on 44 per cent, with Labour on 38 per cent. The Lib Dems trailed on 12 per cent. Experts argue that it is difficult to gauge public opinion precisely in marginal seats, but the trend is clear: where they must win, the Tories are outperforming their national rating.

Labour MPs believe that much of this is due to Lord Ashcroft, who in the 2005 election funded his own operation but under Mr Cameron is an integral part of the Tory campaign.

The Times understands that between 40 and 50 constituencies have been allocated up to £30,000 each, although instalments are being matched to detailed business plans.

Critically, Tory candidates are being encouraged to exploit current rules that allow unlimited spending in constituencies before an election is called. Once an official campaign starts candidates from all parties have a ceiling of £10,000 to £11,000 depending on the population in their constituency.

Labour MPs admitted that they would have started an autumn election at a distinct disadvantage due to lack of funds, with several campaigning with less than £1,000. But many are more concerned that a later poll in 2008, or more likely 2009, would allow Ashcroft money to have a still more significant impact in marginals.

The campaign, coordinated by Lord Ashcroft, follows his mixed success in 2005 when the party gained 33 seats, many of them supported then by his self-funded £1.5 million marginal seats operation. This time the money is even more tightly controlled with candidates asked to account for every penny spent and to fulfil key performance indicators such as regular canvassing and telephoning.

Angie Bray, the Tory party candidate for Ealing Central & Acton, admits that she has been allocated a “generous” amount from the fund, believed to be between £15,000 to £20,000. The tranche received so far has helped to pay for quarterly leaflets and direct mailshots to all households. She is hoping to seize the seat from Labour, which has a notional majority of 800 once the new constituency boundary has been drawn. “But we only get the money if we have been out canvassing, and we have to show the evidence,” Ms Bray said.

Louise Bagshawe, the author and Tory candidate in Corby, is also an Ashcroft beneficiary. She has received thousands of pounds to pay for a direct mailshot and postal vote application forms as well as raising cash locally to pay for a professional agent.

Phil Hope, Cabinet Office Minister and MP for Corby, claims that he does not have the money to match Ms Bagshawe. “I have £750 from donations and no benefactor,” Mr Hope, who has a 1,500 majority, said.

“Louise is loaded and has Ashcroft cash. The West Midlands [Tory] team has at least £50,000,” he said. “All marginal MPs are working extraordinarily hard, talking to Labour and swing voters. But we don’t have the volume to hit them often.

“We can hit them once. The Tories have the cash to hit them at least three times with Ashcroft money.”

Week in Parliament

Today

Commons: Questions to Work and Pensions Ministers, Commons Leader and Commons Commission; Criminal Justice and Immigration Bill, second reading; debate on prepayment water tariffs

Lords: Local Government and Public Involvement in Health Bill, report; debate on new social workers

Tomorrow

Commons: Foreign Office Questions; debate on defence procurement; short debate on antidoping in sport

Lords: Greater London Authority Bill, third reading; UK Borders Bill, report; debate on antiAmericanism

Wednesday

Commons: Welsh Questions; Questions to the Prime Minister; debates opened by Tories on subjects to be announced; short debate on proposals for written constitution

Lords: Local Government and Public Involvement in Health Bill, report; debate on challenges facing NHS in London

Thursday

Commons: Questions on Business, Enterprise and Regulatory Reform and Women and Equality; Greater London Authority Bill, Lords amendments; Further Education and Training Bill, Lords amendments

Lords: UK Borders Bill, report; debate of gambling and sport.

Friday

Commons: Not sitting.

Lords: Building Societies (Funding) and Mutual Societies (Transfer) Bill, third reading; debate on report on sanctions

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