The Footsie index of 100 leading blue-chip stocks is off 7.1 points after an hour's trading to stand at 5410.5.
The London market is suffering another gloomy session following more bad news from the US and a statement from telecoms equipment firm Spirent that the slowdown will depress second-half performance.
Sentiment has been hurt by another sharp fall on Wall Street after GDP figures showed US economic growth had slumped, and just avoided going into negative figures.
Spirent is the Footsie's largest faller, off 12% or 16¼p at 124p, after it announced plans to slash costs by cutting global staff numbers by 500 to help it ride out the tough conditions.
Fellow telecoms equipment firm Marconi has fallen further, and is now off 1p at 58½p.
Tech shares have also slipped, with chip designer ARM Holdings off 11p at 292p; computer services group CMG down 9p at 253p; Logica off 12½p at 706p; and software group Misys down 6p at 330p.
However, there are some rays of hope in the market, with business services group Rentokil Initial jumping 6% or 14¼p at 247p after reporting results in line with market expectations and saying it was upbeat about its future.
On a busy day for corporate results, shares in Hilton Group are up 1¾p to 243½p after it reported a rise in half-year profits.