The FTSE 100 Index was off 85.1 points at 5113.5 as a host of heavyweight stocks dragged the market lower.
Many dealers were reacting to Federal Reserve chairman Alan Greenspan's warning over the state of the US economy on Friday.
The market was also edgy ahead of a clutch of major corporate announcements scheduled for the US later this week.
Tech and telecom stocks were among those losing ground with Vodafone off 4%, or 6½p, at 161p, BT 7½p lower at 246½p and mmO2 down 1¾p at 85p.
Sage also eased 2p at 260p while chip designer Arm fell 11½p at 336p.
Financial and oil shares were among the other leading stocks pushing the market lower.
Shell was down 8¾p at 454¼p, BP shed 4p at 515p and Enterprise Oil, which has been lifted in recent days by takeover speculation, fell back 15½p at 612½p.
HSBC was off 16p at 774p, Lloyds TSB was 13p lower at 713p and Barclays was off 55p at £22.31.
Retail stocks also continued to ease despite another batch of healthy festive trading statements.
GUS said underlying sales at Argos had soared 14% in the 14 weeks to January 5. But luxury brand Burberry - which suffered from falling demand after September 11 - saw sales dip. Shares in GUS lost 7½p at 648p.
Also heading south was Sainsbury's, off 8p at 364½p, despite extra Christmas goods helping like-for-like sales for the six weeks to January 5 rise by 6.8%.