Retail sales grew “strongly” in August and are expected to increase sharply in September, as retailer optimism reaches its highest level since 2002.

Some 51% of respondents reported that sales volumes were up on a year ago, while 14% said they were down. That gives a balance of +37% and matches previous expectations (+36%), according to the quarterly CBI Distributive Trades Survey.

Retailers added that sales were broadly average for the time of year.

Retailers expect sales volume growth to accelerate next month (+42%), with 49% expecting them to rise and 7% to fall. And they were even more optimistic about the next quarter than at any time since May 2002, as retailers ramp up for Christmas.

Barclays head of retail and wholesale Richard Lowe added: “The retail sector has seen increased sales over the summer compared to 2013 and it’s great to see that optimism is so strong. I expect single-digit growth to continue as consumer confidence remains healthy.”

Of the 142 retailers surveyed, sales grew particularly strongly among grocers, chemists and furniture and carpet retailers. But specialist food and drink retailers recorded a fall in sales volumes.

CBI deputy director-general Katja Hall said: “The high streets have been bustling with shoppers this summer and it is good to see firms so optimistic about their business prospects for the next three months - higher than at any time since 2002.

“Retailers looking forward to stronger growth in September are keeping their shelves well-stocked in anticipation.”