A slump in tax receipts is sending the Chancellor's borrowing totals deeper into the red than planned as the economic downturn hits incomes, profits, spending and asset prices, figures released today have indicated.

June figures for the public finances will confirm an increasingly severe toll of tax revenues that is set to force Alistair Darling to borrow more this year and next than he had forecast in his March Budget, The Times believes.

It is thought that today's numbers will reveal that stamp duty receipts are being hit especially hard, and continue to tumble as the housing market downturn means not only falling house prices, but also the fact that far fewer homes are changing hands.

As the housing slump deepens, well-placed sources said that the Treasury fears it could end up losing as much as £5billion of the £13.5 billion that the Chancellor had hoped to rake in from stamp duty payments by homebuyers in the current financial year.

However, it is also understood that other key sources of tax revenue are also being badly hit by the economy's growing deterioration.

Income tax payments are expected to be cut as financial turmoil in the City leads to big reductions in multi-million-pound bonus payments to the Square Mile's bankers, traders and analysts. The impact on corporation tax revenues, too, is expected to be underlined by the June data.

In what is a key month for companies' tax payments, the revenues are expected to be hit as profits from UK plcs drop and as businesses take more steps to limit their tax bills and shore up their financial strength for more difficult times.

Payments of VAT are also set to be squeezed as the downturn leads consumers to curb their spending.

Senior Whitehall figures said that the Treasury is bracing itself for yet worse financial strains on the Government as unemployment climbs, sending welfare payments to people who are out of work spiralling upwards.

While the Chancellor is benefiting, meanwhile, from windfall revenues from the North Sea and on garage forecourts as oil prices keep rising, this was offset this week as Mr Darling was forced to bow to pressure to freeze fuel duty until next April at an initial cost of £550 million.

The Chancellor had already been forced to raise planned government borrowing in the Budget over the period from 2007-08 to 2010-11 by £31.7 billion to nearly £150 billion.

For this financial year, he raised intended borrowing by £13 billion to £43 billion.

Treasury insiders now fear that City economists will be vindicated over warnings that this year's total could hit £50 billion or more, and climb still higher next year, rather than fall back as Mr Darling had factored in.

Officials pointed to the high sensitivity of tax payments by City institutions to economic slowdowns as a key threat to the Chancellor's finances.

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