The BRC said the total value of retail sales between Aug. 30 and Oct. 3 was 3.9 percent higher than in the September period of 2014, the fastest increase since March and much bigger than the 0.1 percent gain recorded in August.

The BRC's figures are not seasonally adjusted, and September figures this year were boosted by back-to-school spending from the late August holiday weekend falling in the September survey period, as well as England hosting the Rugby World Cup.

BRC chief executive officer Helen Dickinson said the growth in sales was likely to be overstated given those factors, but the figures suggest British consumers are continuing to help the economy through a period of weaker growth abroad.

For the third quarter as a whole, retail spending was 2.2 percent up on the year -- stronger than the 1.1 percent recorded in the second quarter, which was affected by the timing of Easter, but slower than the first quarter's 2.8 percent growth.

Furniture, clothing and footwear were the fastest-growing retail sectors. The BRC said autumnal weather boosted demand for seasonal clothing ranges.

Adjusted for falling prices, the BRC said retail sales were up 5.8 percent in September, compared with 3.5 percent sales growth in August in comparable official data.

Spending on a like-for-like basis, a measure which strips out changes in floorspace and is preferred by some equity analysts, rose 2.6 percent year-on-year in September after a 1.0 percent fall in August, the BRC said.

(Reporting by David Milliken; editing by William Schomberg)