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(Noon): The FTSE 100 index was down 8.66 points at 6,575.10 in lunchtime trade with mining stocks weighing on the market.Falling metals prices hit the mining sector, and Rio Tinto shares fell 1.7% after it said first quarter iron ore shipments had dropped 8%.
Brewing giant SABMiller saw its shares slide 1.7% after issuing its latest trading update.
Revenues at the brewer rose 3% in the year to 31 March, missing expectations.
Temporary power provider Aggreko rose 2% after the firm said it had made an "encouraging" start to the year, with underlying revenues up 5% in the three months to 31 March.
Shares in department store chain Debenhams rose 3.8% after the company outlined plans to revive its fortunes.
Debenhams is aiming to improve its online sales offerings and increase the number of brands in its stores.
The plans were unveiled as Debenhams reported a 25% fall in half-year profits to £85.2m, which was in line with the scaled down profit forecast it made in December after weak Christmas sales.
On the currency markets, the pound slipped 0.05% against the dollar to $1.6722 but rose 0.1% against the euro to 1.2117 euros.
