Blue chip shares fell after the European Union set out its approach to Brexit talks, adding that trade talks could begin after "sufficient progress" on a divorce settlement with the UK.
European Council President Donald Tusk in a Brussels press conference said: "Starting parallel talks on all issues at the same time as suggested by some in the UK will not happen."
The FTSE 100 Index was 27.1 points lower at 7342.4 in afternoon trading, as the EU set out a tough line putting talks on trade on hold until the UK has settled its commitments to the bloc, estimated to be as much as €60bn (£51bn; $64bn).
IG market analyst Joshua Mahony said: "This is a clear move to separate the divorce payment from the trade discussions, whereas the UK would obviously see payment as a concession worth bargaining with. The problem is that with valuations over a divorce payments so far apart, there is a feeling that discussions over fees could be protracted."
In London, stocks with exposure to South Africa slumped after President Jacob Zuma dismissed respected finance minister Pravin Gordhan and a number of other ministers in a dramatic overhaul of his cabinet.
Financial services firm Old Mutual was the biggest faller in the top flight falling 8%, or 16.4p to 200.5p. Rival Investec was the biggest faller in the second tier, slumping 9%, or 53p to 551p. Both groups have significant operations in South Africa.
The biggest afternoon risers in the FTSE 100 Index were Direct Line Insurance (+9.7p to 350.7p), Intu Properties (+5.8p to 277.7p), British Land (+12p to 604.5p), Land Securities (+20p to 1047p) and EasyJet (+18p to 1025p).
The biggest afternoon fallers in the FTSE 100 Index were Old Mutual (-16.4p to 200.5p), Mediclinic International (-36p to 723p), Anglo American (-47.5p to 1215p), Antofagasta (-26.5p to 813.5p) and BHP Billiton (-33.5p to 1237p).
The biggest afternoon risers in the FTSE 250 Index were Shawbrook Group (+33.9p to 338.2p), Serco (+6.6p to 117.1p), Entertainment One (+13.8p to 245p), Sports Direct (+12.4p to 307.2p) and Card Factory (+10.3p to 285.4p).
The biggest afternoon fallers in the FTSE 250 Index were Investec (-53p to 551p), Allied Minds (-16.6p to 305p), Clarkson (-111p to 2609p), Ferrexpo (-6.5p to 165.1p) and RPC Group (-30p to 781p).