Campaign spending should be limited at all times, the government says
The government says it will push through measures designed to reduce Tory spending in marginal seats, despite Electoral Commission concerns.
Changes unveiled by Justice Secretary Jack Straw in June would close a loophole allowing supporters to give large sums outside of election periods.
The commission has signalled it has "strong reservations" over this.
But the government said current rules were "ineffective". The Tories said a legal challenge was possible.
Conservative deputy chairman Lord Ashcroft has enraged Labour MPs by putting millions of pounds into target constituencies .
This was credited with securing many of the 33 gains made by the party at the 2005 general election.
Spending during the general election campaign period is limited by law, averaging £11,000 per constituency, depending on its size.
But there are no rules governing how much money can go to promoting candidates outside the official election period.
Under the government's Party Funding Bill, spending would be strictly limited as soon as a candidate was selected.
The bill is to have its second reading in the House of Commons in October.
But in an email circulated to leading figures in all parties over the past few weeks, Mr Wardle warned the set-up would present "problems in terms of uncertainty and scope for avoidance".
He suggested the measures should not be brought into force until the commission had consulted on and finalised its guidance, which could not happen until the bill had been officially passed by Parliament next summer.
That would effectively rule out their introduction before the next general election, which could be as late as May 2010.
Mr Wardle said: "The commission's view is that it would not be able to issue finalised guidance in this area until the relevant primary legislation had received royal assent and the commission had carefully considered the wider context in which guidance would operate, and consulted widely on the content of the guidance."
However, a Ministry of Justice spokeswoman said the measure would "come into effect when the bill receives royal assent. Candidate spending infringements are regulated by the police and the courts."
She denied the government was "at loggerheads" with the commission, saying: "The Electoral Commission acknowledges current rules on campaign funding are ineffective."
A commission spokeswoman said: "We have said for some time that we think the current regulated period for candidate spending is too short, but that any change in the rules would need to address the scope for uncertainty and avoidance.
"It may be possible to achieve this with the right combination of statutory rules and Commission guidance.
"However, we would want to consider any changes carefully to ensure our guidance works with any changes to the law to achieve a fair framework for all candidates."
The commission will set out its response to the Bill "in detail" before it is debated by the Commons, she added.
Tory frontbencher Francis Maude said: "For a governing party to rig election rules just months before an election in order to cling on to power has all the hallmarks of a banana republic.
"It is quite proper for the Electoral Commission to raise concerns over such partisan moves by the government, and there is also a real prospect of a legal challenge in the courts against such flawed new laws."