The London market struggled for direction at the start of the week as the pound strengthened after UK services data rebounded strongly in August. The Markit/CIPS purchasing managers' index (PMI) showed activity in UK services sector jumped to the biggest month-on-month rise in the survey's 20-year history.
The index lifted from 47.4 in July to 52.9 in August. A score above 50 indicates growth.
However, the FTSE 100 Index fell 11.7 points to 6883 in afternoon trading, even as the pound also responded well to the services data, rising 0.6% against the dollar before falling back slightly to just over $1.33.
Chris Beauchamp, chief market analyst at IG, said: "The stronger pound took some of the shine off the FTSE 100, which had looked a touch overextended following Friday's surge, with few big corporate releases this week the market might struggle."
Retailer Marks & Spencer slipped 4p to 350.1p after weekend reports that the group is set to axe around 500 jobs at its London headquarters as the group looks to turnaround its fortunes. Chief executive Steve Rowe, who replaced Marc Bolland in April, is under pressure to cut costs and show how he can improve the chain's long-running poor sales figures at its key clothing division.
In afternoon trading the biggest risers on the FTSE 100 Index were Randgold Resources (+185p to 7650p), CRH (+48p to 2585p), Paddy Power Betfair (+150p to 9165p), Fresnillo (+27p to 1695p) and BAE Systems (+8p to 556p).
The biggest fallers on the FTSE 100 Index were Royal Bank of Scotland (-7p to 197.3p), Provident Financial (-84p to 3016p), Lloyds Banking Group (-1.3p to 59.7p), Intu Properties (-6.3p to 306.1p) and Worldpay Group (-5.2p to 293p).
In afternoon trading the biggest risers on the FTSE 250 Index were Zoopla (+24.7p to 330.7p), Dechra Pharmaceuticals (+70p to 1370p), Evraz (+6.4p to 134.3p), Acacia Mining (+20p to 504p) and Kaz Minerals (+6.6p to 184.7p).
The biggest fallers on the FTSE 250 Index were Virgin Money Holdings (-12.6p to 305p), Redefine International (-1.43p to 42.1p), Tritax Big Box Reit (-3.8p to 144.3p), Hastings Group (-5.6p to 220.8p) and N. Brown (-5.3p to 211p).