Shadow Housing Minister Grant Shapps comments on a £25 million "black hole" in flagship Government plans to build new affordable and social housing.
Last summer Gordon Brown announced moves to build 110,000 new homes by reallocating funds from existing projects.
£183 million was due to be found through "efficient and flexible management" of housing and regeneration programmes, but Housing minister John Healey has now said £25 million has yet to be identified.
"The Prime Minister is once again guilty of a financial sleight of hand. We've seen it before on the 10p tax scandal and he should know it always comes back to haunt him", Grant Shapps said.
Healey revealed efficiencies for 2010-11 would be found "at a later stage, following an assessment of performance and delivery options". But Shapps said this was "grossly irresponsible" and was likely to mean further borrowing to plug the shortfall.
"Gordon Brown is responsible for plunging this country into the red to such an extent that we risk losing our economic sovereignty and yet funds his latest initiative with millions of pounds that ministers have admitted they will worry about after the election", he said. "Under Labour that's likely to mean even more borrowing."
"This is grossly irresponsible and just goes to prove that it's time to get rid of Labour and elect a government that will take decisions based on the long-term needs of Britain, not on short-term electoral calculations."