Blue chip shares were on the front foot despite the political chaos of a hung parliament following the UK general election.
Conservative British Prime Theresa May lost her majority in Parliament after the country went to the polls on Thursday (8 June).
The Tories now face having to govern in a minority administration with the support of the fringe Democratic Unionists of Northern Ireland.
The FTSE 100 Index lifted 36.3 points to 7486.2 in afternoon trading, as heavyweight commodity stocks helped the London market shrug off the shock of the Conservatives failure to win the election. the FTSE 250 dipped 110.7 points to 19632.7.
Stocks also rose as the pound fell by almost 2% against the dollar and the euro at one point, as the international exporters in the Footsie were buoyed by weaker sterling values.
CMC Markets analyst David Madden said: "The pound has plunged against the US dollar and the euro due to the lack of a Conservative majority.
"The collapse in the pound in the wake of the hung parliament is the main driver behind the rally in the FTSE 100, as the index has such large international exposure."
The biggest afternoon risers in the FTSE 100 Index were Fresnillo (+75p to 1740p), Randgold Resources (+175p to 7670p), Smurfit Kappa (+44p to 2211p), Scottish Mortgage Investment Trust (+8.1p to 416.1p) and Croda International (+64p to 3958p).
The biggest afternoon fallers in the FTSE 100 Index were Royal Bank of Scotland (-8p to 249.3p), Barratt Developments (-17.5p to 572.5p), Taylor Wimpey (-5.1p to 178.4p), Persimmon (-61p to 2350p) and Babcock International (-22p to 887p).
The biggest afternoon risers in the FTSE 250 Index were Hochschild Mining (+12p to 313.6p), Centamin (+6.2p to 178.5p), Kaz Minerals (+17.8p to 517.5p), Ashmore Group (+9.3p to 358.5p) and Genesis Emerging Markets Fund (+13p to 670p).
The biggest afternoon fallers in the FTSE 250 Index were OneSavings Bank (-19.3p to 400.8p), Crest Nicholson (-28p to 582.5p), Virgin Money (-13.4p to 279p), Nostrum Oil & Gas (-21p to 504p) and Travis Perkins (-63p to 1542p).