Market researcher Kantar said the growth was down from 18.9% in last month's report, with the data suggesting shoppers were cautiously returning to pre-lockdown behaviours.

The government allowed pubs, cafes and restaurants in England to reopen on July 4, giving people an alternative to eating at home.

"As lockdown restrictions are gradually eased and non-essential retail outlets re-open, some consumers are slowly resuming their pre-Covid routines and shopping habits," said Fraser McKevitt, Kantar's head of retail and consumer insight.

But he said normality was still a long way off. Shopper visits to supermarkets were still 15% lower and the average spend per trip was 25.05 pounds ($31.74), 35% more than the same period last year, as people continue to eat more at home.

Online sales rose 92%, accounting for 13% of all grocery sales.

Of Britain's big four grocers No. 4 Morrisons was the best performer over the 12 weeks to July 12 with sales growth of 17.4% and a market share gain for the first time since 2015. Morrisons shares were up 1.3% at 0817 GMT.

Market leader Tesco achieved growth of 15.1%, followed by Sainsbury's on 13.5%. Walmart owned Asda was the laggard again with growth of 11%.

The big four's growth was dwarfed by Iceland, whose sales surged 34.1% as shoppers bought more frozen food.

German-owned discounters Aldi and Lidl saw sales growth of 13% and 17.3% respectively, though as was the case in last month's report Aldi's market share did fall.

Kantar said grocery inflation was 3.6% over the 12 weeks, with prices rising fastest in markets such as cooking sauces, fresh bacon  and canned colas while falling in fresh poultry, butter and bread.

By James Davey