Paul Johnson, director of the Institute for Fiscal Studies, said there is a risk that the Government's Help to Buy scheme, designed to make houses more affordable, could have the opposite effect.
Speaking to Economics Editor Richard Edgar, he said: "There is a risk that a lot of this will do more to push prices up rather than making things more affordable."
He added that the policy is a "distributional" one as it helps those without large deposits get on the housing ladder, but in some cases "that's a bigger risk".
George Osborne faces criticism that his mortgage guarantee plan might actually make houses less affordable.
The Treasury has still not explicitly said it will prevent homeowners from using taxpayer-backed Mortgage Guarantees to buy second homes.
It opens up the possibility of buying a house to millions who don't have a deposit but they might have to pay more for the privilege.