Blue chip shares struggled for direction despite a Supreme Court ruling that Parliament must vote on whether the Government can trigger the Brexit process.
The FTSE 100 Index edged up 12.5 points to 7163.6, although the pound reacted more strongly, falling 0.6% against the dollar at 1.246 and was 0.4% lower against the euro at 1.159. The FTSE 250 slipped 13.5 points to 18102.5.
In the top flight, shares in BT plunged after it issued a profit warning after revising up the impact of an accounting scandal at its Italian business by more than three times to £530m ($661m, €615m), from £145m three months ago.
The telecoms giant now said: "The extent and complexity of inappropriate behaviour in the Italian business were far greater than previously identified."
Spreadex financial analyst Connor Campbell added: "The telecoms giant continued to plunge by 18% following the surprise statement about the costly Italian accounting nightmare, with chief executive Gavin Patterson piling on the misery by stating that the UK market is slowing during a post-update conference call."
BT shares fell 72.6p to 310p.
The biggest risers in the FTSE 100 Index were Anglo American (+71.5p to 1380p), ITV (+9.4p to 210.7p), Rio Tinto (+153p to 3627.5p), BHP Billiton (+60.5p to 1498p) and Antofagasta (+29.5p to 819p).
The biggest fallers in the FTSE 100 Index were BT (-72.6p to 310p), EasyJet (-95p to 981p), Dixons Carphone (-13.6p to 322.5p), Paddy Power Betfair (-245p to 8050p) and Capita (-14p to 508p).
The biggest risers in the FTSE 250 Index were Kaz Minerals (+19p to 442.3p), Evraz (+9p to 233p), Renishaw (+106p to 2827p), Vedanta Resources (+28p to 1043p) and Ferrexpo (+3.1p to 139.7p).
The biggest fallers in the FTSE 250 Index were PZ Cussons (-34.8p to 301.7p), William Hill (-14p to263p), TalkTalk (-5.8p to157.6p), IG Group (-17p to524p) and BTG (-17.5p to556p).