The FTSE 100 slipped from 10-week highs by mid-session as the drugs sector fell after yesterday's setback for a key AstraZeneca drug.
AstraZeneca slid 5.5 per cent today, dragging down rival GlaxoSmithKline by 2.9 per cent, in a second day of falls as analysts downgraded the shares after news that Astrazeneca's lung cancer drug Iressa was not as effective as hoped.
The drugs sector accounted for most of the FTSE 100's 27.9-point fall to 4,398.9 in afternoon action, with the index breaking a three-session winning streak which had carried it up to 4,452.4 - its highest level since July 10th.
But WPP, the world's largest advertising company, was top FTSE loser, down 6.2 per cent to 469 pence after it warned that recovery might not come through until next year at the earliest as it reported a sharp fall in profits.
The advertiser's profit figures came in broadly in line with forecasts, but helped prompt investment bank Merrill Lynch to cut its 12-month price target to 700 pence from 760 pence.
Oil stocks stood out against the overall trend, however, with BP up 1.7 per cent and Shell adding 1 per cent as crude oil futures prices held firm just below $30 a barrel, ahead of data expected to show a fall in US oil stocks.
Television group Granada was the FTSE 100's biggest gainer for a second day, up 5.1 per cent on news on Monday it would work with Carlton Communications on programme scheduling and marketing to boost advertising revenues and viewers.