The UK market was on track for its worst week in two months as retail shares continued to lose ground.
Shortly after midday, the benchmark FTSE 100 share index was down 39.97 points at 7,444.13.
Retail distribution group Bunzl was the biggest faller in the index, down more than 6%, after Morgan Stanley flagged up the risk to the company from Amazon's business-to-business venture.
Burberry shares fell again, dropping nearly 4%.
On Thursday, shares in the luxury fashion group had sunk 10% after it unveiled plans to move further upmarket.
Marks and Spencer fell 1.6% and Primark owner AB Foods was down 1.8% as investors digested a week of downbeat retail news.
In the FTSE 250, Ultra Electronics fell more than 7% after the defence firm said a decision on its purchase of US firm Sparton was set to be delayed.
Ultra Electronics announced in July it would buy Sparton, which makes anti-submarine devices, for $234m.
However, it said in September that the US Department of Justice had asked for more information, and it now expects the department to make a decision at the end of March.
On the currency markets, the pound was up 0.3% against the dollar at $1.3182 and was also 0.3% higher against the euro at €1.1324.