The FTSE 100 index was down 73.57 at 6,112.02 points.
Mining companies saw some of the biggest falls as the price of metals declined.
The biggest faller on the FTSE 100 was mining giant Rangold, whose shares lost 11%. Fellow BHP Billiton, was down 6%, with its shares also being affected by news of a lawsuit in Brazil.
Federal prosecutors in Brazil have filed a $43.5bn (£30bn) civil lawsuit against iron miner Samarco and its owners BHP and Vale, over the collapse of a dam last year that killed 19 people.
Shares in Sainsbury's  extended losses throughout the afternoon to lose 6% after the supermarket reported a fall in underlying full-year profits.
Profits fell to £587m from £681m in the previous year as the supermarket price war continued to have an impact.
Shares in rivals Tesco and Morrisons were also lower, with Tesco down 5% and Morrisons 1.7%, as research from Kantar Worldpanel indicated that all the big four supermarkets had lost market share in the 12 weeks to 24 April.
Next shares rose 3.5% despite the retailer cutting its full-year sales and profit forecasts on fears of a slowdown in consumer spending.
On the currency markets, the pound slipped 0.4% against the dollar to $1.4478, and was 0.3% lower  against the euro at €1.2593.

The office in Cowbridge Road has been closed with a note placed on the window advising claimants and jobseekers where to go instead.
The Department for Work and Pensions (DWP) confirmed the incident.
A Public and Commercial Services union spokesman has claimed several workers had oxygen therapy after a suspected carbon monoxide leak.
(Close): London's top share index closed down 1.2% as mining and supermarket shares fell.
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Some members of staff at a Jobcentre in Cardiff have been sent to hospital following a gas leak.