The London market was higher in afternoon trading as shoppers shrugged off the effect of the country's Brexit vote, leading high street spending to smash forecasts in July.
Figures from the Office for National Statistics said retail sales volume growth jumped by 1.4% in July compared to a year ago, buoyed by department store and fashion trading.
The FTSE 100 Index edged up 5.4 points to 6864.6, with the survey well above economists' estimates of a 0.1% rise in July. The FTSE 250 rose 71.3 points to 17830.
Spreadex financial analyst Connor Campbell said July retail sales exceeded expectations and had taken the Footsie by "surprise".
In the second tier, oil and gas explorer Premier Oil swung to a profit in the first six months of its financial year and lifted its full-year guidance on the back of what it called a very solid performance.
The London-listed firm posted a profit after tax of $167.1m (£127m) in the six months to the end of June, compared with a $375.2m loss in the year before. Shares rose 2p to 78.5p.
In afternoon trading the biggest risers on the FTSE 100 Index were Antofagasta (+21.5p to 564p), Persimmon (+56p to 1804p), Barratt Developments (+13p to 461.2p), BHP Billiton (+27.5p to 1073.5p) and Taylor Wimpey (+4p to 157p).
The biggest fallers on the FTSE 100 Index were Pearson (-20.5p to 862p), British American Tobacco (-88.5p to4858.5p), Legal & General Group (-2.9p to207.7p), CRH (-32p to2503p) and Royal Bank of Scotland (-2.3p to 188p).
In afternoon trading the biggest risers on the FTSE 250 Index were Kaz Minerals (+17.4p to 181.1p), Hays (+5.1p to 127.3p), ICAP (+15.7p to 474.6p), Thomas Cook (+2p to 63.5p) and Bellway (+67p to 2217p).
The biggest fallers on the FTSE 250 Index were Evraz (-17.7p to 155.2p), Laird (-12.3p to 295.7p), Card Factory (-9.3p to 280.2p), Rank Group (-6.7p to 217.2p) and Fidelity European Values (-3.5p to 176.4p).