The FTSE has started the day in the red after Ben Bernanke's cautious comments overnight hit sentiment on Wall Street.
The Dow Jones industrial index closed down more than 1% at 10120.5 after
the Federal Reserve chairman warned that the US economy faced "unusually uncertain" prospects, and said the central bank was ready to take further steps to bolster growth if needed.
The FTSE is currently down around 20 points, or 0.4%, at 5195 and stock markets in France and Germany are also in the red.
There was further pressure on Wall Street as Barack Obama signed into law the biggest overhaul of financial regulations since the Great Depression.
On the FTSE 100, the top faller was Autonomy, the software search specialist, after its trading update left analysts downbeat. The company reported a 7% rise in earnings per share to $0.28 in the three months to June 30 from a year ago and noted a "gentle recovery" during the first half.
Chief executive Mike Lynch commented:
"In considering the macro environment our customers are positive but still cautious."
"Overall we face the rest of the year with a strong balance sheet, and in light of the continuing macro recovery, we are confident in our ability to continue to deliver strong growth for the full year."
The shares were down more than 8% at £16.63.
Analyst Julian Yates at Investec keeps a "hold" recommendation on the shares, cites concerns about gross margins deteriorating and comments:
"While still at respectable levels, we would argue the valuation demands higher growth, or signs of material upwards forecast momentum, which (aside of M&A) is not immediately apparent in this statement."
