Brown's housing cash to come from Decent Homes, health and M25

The government is already being challenged over where it plans to raise the finance from a package of measures launched in Parliament yesterday which will see the construction of 30,000 extra "social homes."

The Times reported departments appeared not to be aware last night that they were helping to fund the £1.5bn centrepiece of the government's election fightback, "Building Britain's Future".

Downing Street said that the half cost of building a total of 110,000 social homes over the next two years would come from the Department for Communities, with the rest made up from "underspends" elsewhere.

But the paper said that the Department for Communities appeared to be fighting the idea that it would foot such a large proportion of the bill, which could see its Decent Homes refurbishment budget raided.

The Schools Department was also taken by surprise, according to the report.

Meanwhile the Department for Health indicated that the money could come from a £350m underspend in capital projects this year.

And the Department for Transport indicated that the money would be raised from underspending on the M25 widening scheme.