Uncertainty over global growth dragged on investor sentiment in early trading along with a a renewed surge in oil prices.
Brent crude climbed back up near $124 a barrel as another refiner announced cuts to Iranian imports, feeding fears of a supply crunch as the West presses ahead with sanctions on Tehran.
Copper prices, however, edged lower, falling back after hitting one-month highs, with mixed data from China creating uncertainty.
The country said it aims to grow its economy by 7.5 per cent in 2012 - down from eight per cent.
That sparked fears that the engine room of world economic growth was stuttering.
Meanwhile Britain's services sector grew less than expected in February, but still indicated the economy is picking up after a slump late last year, a survey showed.
The Markit/CIPS Purchasing Managers' Index (PMI) for services fell to 53.8 from 56.0 in January, which had been a 10-month peak
Miners and engineers were the biggest hit stocks on the FTSE 100.
Engineer GKN was the biggest faller, down 3.8 per cent, while IMI was off by 3.7 per cent.
Weir group — which is fighting a rival in a takeover struggle for the firm Ludowici in Australia — dipped by 3.7 per cent.
Other significant fallers included India-focused Essar Energy, down 3.2 per cent and and miner Rio Tinto, off by 2.2 per cent.
Commodities giant Glencore was off by 0.8 per cent. It reported a rise in profits in its full-year preliminary results for 2011 and said its $37bn bid for Xstrata was "fair" for all parties.
On the positive side safety testing giant Intertek was the highest climber, up 2.1 per cent after reporting a profits rise.
BP nudged up by more than two per cent after announcing that it had come to an out-of-court settlement in connection with compensation claims for the Gulf of Mexico spill.
Oil services company Petrofac was up more than one per cent after reporting strong results to the market. Drinks giant Diageo was another gainer, edging up by 0.7 per cent.
On the FTSE 250 insurer Amlin was down by five per cent after reporting a loss triggered by a surge in catastrophe claims across the globe