Dozens of senior councillors from all three parties have publicly complained that government plans to provide free home care are flawed and will force cuts to current services.

In a letter to The Times, the councillors say they support the principle of providing additional support to those with the most critical care needs but Gordon Brown’s proposed legislation “has major weaknesses and risks adding further strain to an existing system already under considerable financial pressure”.

It comes as no coincidence that a general election is just around the corner and then suddenly all these promises are appearing

It concludes: “It is also wrong to raise expectations among many of the most vulnerable in our society and their families that they may be in a position to benefit from these proposals when the reality may be significantly different.”

The letter’s leading signatory is David Finch, the Conservative chairman of social care at Essex county council, while the other 77 also have responsibility for social care. Five are Labour councillors.

Cllr Finch told The Times: “It’s not that the idea is not valid. It is that the way it is being implemented has not been thought through in any way. This is going to mean funds are diverted from needy adult social care services in order to finance this package.

“[The government] is providing the public with all sorts of goodies. It comes as no coincidence that a general election is just around the corner and then suddenly all these promises are appearing,” Cllr Finch added.

The annual cost of the bill is put at £670m. Of this total, £420m is to come from existing Department of Health budgets, with local authorities told that they must provide the remaining £250m from efficiency savings.

But, as LGC has reported, the proposals, unveiled by Mr Brown at the 2009 Labour Party conference, have already been criticised as underfunded by the Association of Directors of Adult Social Services.

It suggested a minimum £330m shortfall between the government estimates and the real demands on the system - which councils would have to bear, more than doubling the projected £250m costs to local authorities.

The Association of South East Strategic Leaders and South East Councils Adult Social Care has predicted that the cost to authorities in that region alone would be £100m a year.

Care services minister Phil Hope told the Times it was “extremely disappointing” that councillors supported the principles of the bill, but would “quibble and complain and find reasons not to make it happen”.

“Care recipients in these council areas will be shocked that local authorities are apparently unable to find efficiencies to deliver this priority when significant funding is being provided by the government,” he said.