Blue chip shares hit another record high as the pound slumped following comments from Prime Minister Theresa May on Brexit.
May dismissed the idea that the UK could "keep bits of membership" of the EU during a weekend TV interview, raising the prospect of a so-called "hard Brexit".
The FTSE 100 Index lifted 19.2 points to 7229.3, after having peaked at a record mid-session high of 7240 as sterling fell by 1% against a basket of currencies.
Top flight shares are more appealing to investors when the pound slides because most of these firm's sales are earned aboard, boosting revenues when translated back into sterling.
The Footsie has hit a series of highs in recent weeks driven by the pound, which has fallen some 18% against the dollar and 11% against the euro since June's Brexit vote.
The FTSE 250 Index rose 6.9 points to 18348.
In the second tier, William Hill fell 4.9p to 292.8p, after the UK's largest bookmaker said punters winning £20m ($24m) in December on football and horseracing results meant its full-year estimates would come in at the bottom end of expectations.
The firm blamed unfavourable results at the end of last year for its annual operating profit estimates coming in at around £260m, the lower end of its £260-280m range.
Boxing Day blues
The betting group said the Boxing Day football programme was the worst weekend on record with 18 out of the top 20 best backed teams winning.
It added that horseracing during the Christmas period was also bad for bookies. A large number of favourites won races including the King George VI Chase, won by favourite Thistlecrack and the Welsh Grand National the following day, was also won by favourite Native River.
The biggest risers in the FTSE 100 Index were Glencore (+7.5p to 296p), Sage Group (+14p to 671.5p), Anglo American (+20.5p to 1155.5p), Burberry Group (+26p to 1499p) and Imperial Brands (+55.5p to 3594p).
The biggest fallers in the FTSE 100 Index were Land Securities (-27p to 1030p), Capita (-12.5p to 503p), Royal Bank of Scotland (-5.3p to 227.1p), British Land (-11.5p to 625p) and Intu Properties (-4.7p to 277p).
The biggest risers in the FTSE 250 Index were Ferrexpo (+6.4p to 136p), CMC Markets (+3.8p to 124.6p), Indivior (+9.1p to307p), Electrocomponents (+12.5p to487.6p) and Petrofac (+21.5p to920.5p).
The biggest fallers in the FTSE 250 Index were Ashmore (-16p to 283.4p), Evraz (-7.7p to 207p), Derwent London (-75p to 2685p), Grafton Group (-14.5p to 546.5p) and Workspace Group (-18.5p to 779.5p).