Economists last night gave warning that further turbulence in stock markets this week could hit growth in the world’s leading industrial economies, after share prices on both sides of the Atlantic tumbled last week.

The FTSE 100 has lost more than a tenth of its value in a month. Commentators are concerned that any further moves this week by central banks to inject further capital into the banking system “may not be sufficient to quickly restore calm in the markets”.

The warning came as American economists sought to reduce their forecasts for growth, with the US economy predicted to stagnate in the second half of this year and the Federal Reserve Bank under increasing pressure to cut interest rates. There is growing speculation in New York that, should the market turbulence get worse, the Fed might even be compelled to cut rates outside its normal scheduled meetings.

Carl Weinberg, of High Frequency Economics, said that he is reducing his forecast for US GDP as a result of the turbulence in the markets. He said that he is now predicting “zero growth” in the second half of the year.

Last week, stock markets in London, New York, Japan and Australia lost as much as 8 per cent of their values on fears over the extent of large banks’ exposure to losses in the American sub-prime mortgage market.

About $1.3 trillion (£642 billion) worth of sub-prime home loans were sliced up, repackaged and sold on to banks and hedge funds. Defaults triggered losses on the investments.

Central banks across the world were forced to inject capital into the banking system, with the European Central Bank offering €96 billion (£65 billion) of emergency aid and the US Federal Reserve Bank injecting $35 billion (£17 billion) to stabilise overnight markets for lending between banks.

Larry Hatheway, chief economist at UBS, the investment bank, said: “Deleveraging may prove longer lasting and not confined to the US sub-prime mortgage market. Concerns about where losses and even insolvency may crop up are likely to plague markets for longer.”

The Bank of England has yet to intervene in Britain’s sterling overnight money market despite jumps in sterling interest rates for overnight interbank borrowing. Compared with the Bank’s 5.75 per cent base rate, the so-called sterling Libor overnight rate has moved up dramatically, jumping from 5.85 per cent on Wednesday, to 6.165 per cent on Thursday, and then to 6.475 per cent on Friday. Analysts believe it is impossible to rule out intervention by the Bank to curb this rise in the cost of overnight borrowing between commercial banks.

Yesterday, the British Chambers of Commerce was already predicting that the UK economy is preparing to experience a “marked slowdown” after five interest rate rises since August 2006.

Lawrence Staden, principal of GLC, a hedge fund, said: “Nobody has yet mentioned to me the possibility of a stock market crash and I find that surprising. I don’t think we are looking at interest rate cuts yet, but the central banks are going to have to inject as much liquidity as necessary back into the markets.”

Investment bankers spent an anxious weekend trying to shore up billions of pounds worth of financing not yet finalised for pending deals.

Robert Tchenguiz, the billionaire property tycoon, has been forced to delay a £1.79 billion refinancing of Somerfield, the UK supermarket group, at least until September as banks pulled down the shutters on new lending.

There is also speculation that Delta Two, the Qatari investment fund stalking J Sainsbury, will be forced to increase the amount of equity in its £10.6 billion bid proposal for the UK supermarket group.

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