Top flight stocks on London lifted in afternoon trading after the pound dived on Asian markets with automated trading blamed for the volatility.
Sterling at one stage overnight fell as much as 6% to $1.1841 – the biggest move since the Brexit vote in June – before recovering. It is currently 1.6% lower at $1.2420.
The FTSE 100 Index lifted 50.6 points to 7050.6, after the crash which came after the Financial Times published a story online about French President Francois Hollande demanding "tough Brexit negotiations".
Analysts say the slump could have been caused by automated trading systems reacting to the report. The Bank of England added it was "looking into" the flash crash.
IG market analyst Joshua Mahony said: "Traders woke up to yet another reminder of the fragility of financial markets, with sterling staging a flash crash overnight, tumbling 6% and then bouncing in quick succession."
Mining stocks such as BHP Billiton and Anglo American, rallied as a result of a weaker pound.
Shares in housing firms fell after Halifax data showed a slowdown in the market. Barratt Developments, Taylor Wimpey and Persimmon were all lower.
In afternoon trading the biggest risers in the FTSE 100 Index were Randgold Resources (+370p to 7,255p), Fresnillo (+85p to 1,699p), BHP Billiton (+37.5p to 1,239.5p) and Mediclinic International (+25.5p to 914.5p).
The biggest fallers in the FTSE 100 Index were Next (-263p to 4484p), Barratt Developments (-28p to 477.1p), Lloyds Banking Group (-2.9p to 52.1p), Taylor Wimpey (-7.8p to 145.6p) and Persimmon (-90p to 1733p).
In afternoon trading the biggest risers in the FTSE 250 Index were Hochschild Mining (+17p to 266.8p), Evraz (+12.2p to 197.2p), Acacia Mining (+29.7p to 489.6p), Centamin (+8.1p to 153.4p) and Kaz Minerals (+10.7p to 243p).
The biggest fallers in the FTSE 250 Index were DFS Furniture (-18.2p to 255.1p), Aldermore Group (-12.3p to 180p), OneSavings Bank (-17.5p to 272.5p), Fidessa Group (-145p to 2319p) and Sports Direct International (-17.4p to 283p).