Blue chip shares struggled for direction with European markets largely flat a day after the UK triggered Article 50, beginning moves to leave the European Union.
The FTSE 100 Index slipped 17.1 points to 7356.6 in afternoon trading, giving up the modest gains it made yesterday. The FTSE 250 fell 8.8 points to 18970.
Germany's Dax and the Cac 40 in France were both slightly higher.
IG chief market analyst Chris Beauchampm said: "When Article 50 day is not particularly exciting, it doesn't bode well for the following day. Markets remain quiet, as investors continue to search around for a reason to buy into equities."
In a quiet session for corporate news Scottish energy supplier SSE said it expects operating profit in its networks division to be around £100m lower next year.
It added that changes in the gas distribution revenue earned by its SGN unit are likely to reduce its operating profit contribution to SSE by around £20m, after taking account of the group's sale of a 16.7% stake in the division.
SSE shares fell almost 2%, or 27p to 1461p.
The biggest afternoon risers in the FTSE 100 Index were Ashtead Group (+50p to 1688p), Coca-Cola HBC (+32p to 2065p), Smurfit Kappa Group (+31p to 2161p), Morrisons (+3.4p to 240.6p) and InterContinental Hotels (+54p to 3901p).
The biggest afternoon fallers in the FTSE 100 Index were Schroders (-78p to 3016p), BT (-7.1p to 315.3p), Marks & Spencer (-7p to 328.5p), British Land (-12p to 590p) and SSE (-27p to 1461p).
The biggest afternoon risers in the FTSE 250 Index were Petra Diamonds (+9.2p to 133p), Euromoney Institutional Investor (+43p to 1081p), Tullow Oil (+8.8p to 228.8p), Polypipe Group (+12.7p to 366p) and Weir Group (+57p to 1933p).
The biggest afternoon fallers in the FTSE 250 Index were Clarkson (-144p to 2731p), Kier Group (-55p to 1359p), Phoenix Group (-30p to 745.5p), RPC Group (-34p to 845p) and Capital & Counties Properties (-6.2p to 281.6p).