Gordon Brown's planned economic package next month will push public finances dangerously into the red and make it harder for the Bank of England to cut interest rates, experts say.

They warn that the soaring budget deficit, which could top £60 billion, leaves the prime minister and chancellor no room for manoeuvre.

Political pressure on Brown and Alistair Darling has intensified with the news last week that the economy stagnated in the second quarter of the year and appears to be on the brink of recession.

The government’s rescue of Northern Rock will also come under renewed scrutiny with revelations in The Sunday Times today that the Treasury was advised by Goldman Sachs, the investment bank, that nationalising Northern Rock would leave taxpayers with a loss of at least £450m and possibly more than £1 billion. Earlier this month the government announced an additional cash injection of £3 billion for the mortgage bank.

Brown dropped hints on his trip to the Beijing Olympics that the government would introduce measures next month to boost the economy.

Among the options are a one-off payment to families to ease the burden of rising food and fuel bills. There will also be a package to revitalise the housing market, including a possible temporary suspension of stamp duty, increased public spending on buying unsold new homes and measures to free up the mortgage market after a collapse in lending.

However, some economists say the package, which could cost several billion pounds, would make a mockery of the government’s fiscal rules. “I’m afraid we’re going to see a lot more borrowing and spending,” said Peter Spencer, economic adviser to the Ernst & Young Item Club, which uses the Treasury’s model of the economy.

“It is one reason why the Bank of England is reluctant to cut interest rates. They want to see the colour of the government’s money.”

Robert Chote, director of the Institute for Fiscal Studies, said it was hard to see how the Treasury could announce a big giveaway and claim it was serious about its fiscal rules.

“Gordon Brown’s transfer from gamekeeper to poacher has seen a major loss of credibility,” he said.

John Hawksworth, an economist at Price Waterhouse Coopers, said: “It is hard to see much scope for anything when the budget deficit is already so large.”

Earlier this month the International Monetary Fund called on the government to act to bring down the budget deficit, including reversing next year the £2.7 billion giveaway that Darling had announced in May to buy off the backbench opponents of the abolition of the 10p starting rate of tax.

The Conservatives have repeatedly pressed the government to publish the Goldman Sachs advice on Northern Rock to the Treasury.

George Osborne, the shadow chancellor, said: “We are beginning to see the true cost to the taxpayer of Gordon Brown’s dithering over Northern Rock. In public he told us that no taxpayers’ money would be at risk, in private his bankers were telling him that hundreds of millions of pounds were at stake.”

John McFall, the Labour chairman of the Commons’ Treasury select committee, admitted that “tight times” in the mortgage market would have an impact on the government’s ability to keep its promises over Northern Rock.

He said: “It makes the commitment to ensure the taxpayer doesn’t lose out harder.”

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