((This version of the September 20 story corrects paragraph 6 on likelihood of flat Q3 retail sales, after ONS corrects estimate given to media))
By David Milliken
LONDON (Reuters) - British retail sales unexpectedly surged in August, official figures showed on Wednesday, boosting the chance that the Bank of England will raise interest rates in November.
Last week the BoE said it was likely to raise interest rates in the coming months if the economy and inflation pressures strengthen as expected.
Wednesday's official data showed a sharp pick-up in monthly sales growth in August to its fastest since April, despite inflation pressures that have previously squeezed spending.
Retail sales volumes rose 1.0 percent month-on-month, beating all economists' forecasts in a Reuters poll, and July's sales growth was revised up to 0.6 percent.
Looking at the three months to August as a whole, which smoothes out monthly volatility in the data, sales growth versus the previous three months rose to 1.2 percent from a three-monthly rate of 0.7 percent in July.
The ONS said sales would need to fall at least 2.9 percent in September for there to be no third-quarter growth overall.
BoE policymakers expect moderate third-quarter retail sales growth as consumer demand shows signs of improving after weakness earlier in the year, though they said it was too soon to tell if it would compensate for weak business investment.
Compared with a year earlier, sales in August were up 2.4 percent versus expectations of a 1.1 percent rise.
"Within this month's retail sales we are seeing strong price increases.... However, we are still seeing underlying growth in sales volumes, and with strong growth in non-essential purchases," ONS statistician Kate Davies said.
Rising inflation has eaten into British consumers' disposable income this year, causing the weakest first quarter for retail sales since 2010, as the fall in the pound after last year's Brexit vote pushed up the cost of the imports.
The measure of inflation used in retail sales data rose to an annual rate of 3.2 percent in August, up from 2.7 percent. Looking just at goods sold in non-food stores, inflation was its highest since March 1992.
Official data last week showed that wages in the three months to July were 0.4 percent lower in real terms than in 2016, and a survey of households by financial data company Markit reported the biggest squeeze in three years in the three months to September.
Private-sector figures had given a mixed message on retail spending in August. The Confederation of British Industry reported the weakest performance since July 2016, while the British Retail Consortium said top-line growth was the fastest so far this year.
The BoE expects inflation to peak at just over 3 percent in October, compared with 2.9 percent now, and then fall slowly.
British fashion retail firm French Connection Group Plc (L:FCCN) reported on Tuesday that it had seen momentum build in recent months despite difficult trading conditions.
Larger rival Next (L:NXT) raised profit forecasts last week and said it expected price rises of no more than 2 percent in the first half of 2018 and none in the second half, if the pound stays stable.
The ONS said non-food retailing and online drove retail sales growth in August, at the expense of purchases of food. Growth was partly driven by sales of watches and jewellery.