Warmer weather and the Olympics – as well as heavy vouchering – helped grocers to their best trading performance of the year last month.

Grocery sales in the four weeks to 18 August were up 3.5% over the equivalent period last year, according to new data from Nielsen.

Volumes were up 1.7% – ending 18 consecutive months of declining volumes.

Tesco continued its recent improved performance, growing sales for the 12 weeks to 18 August by 4%, ahead of the market. But Waitrose emerged as the biggest winner of the period with growth of more than 9%.

“Although promotional activity has remained unchanged at 35% of FMCG sales, the continual use of money-off vouchers and coupons has marked a differing approach by retailers this summer,” said Nielsen’s Mike Watkins.

“This has helped to increase shopping basket spends and, in return, given shoppers further savings at the checkout. Tesco, in particular, had some very attractive offers during July and August, which will have helped to increase the frequency of shoppers’ visits.”

Watkins added: “The Tesco sales recovery we first saw last month has continued and Tesco has now held market share at 29.1% over the last 12 weeks.

“Discounters continue to grow sales faster than other food retailers, while Waitrose outperformed with a stellar sales growth of 12% in the four weeks to 18 August – helped by shoppers spending more per visit on food and drink – making them this period’s winner across the supermarket sector.”