Upmarket grocer Waitrose has defied the squeeze on consumer spending to deliver an 11.1% rise in first-quarter sales.

The supermarket, part of the employee-owned John Lewis Partnership, said most of its growth during the three months to the end of April came from existing stores, as only one new store opened during the period.

Its online grocery sales surged 50.1% during the quarter. For the first time more than five million customers visited its branches per week, the retailer said, and customer transactions were up 8.4%.

Waitrose finance director Tom Athron said the chain was competing effectively with its bigger rivals Tesco and Sainsbury's on pricing, while its extended brand price match helped it win new customers.

Mr Athron said: "In a challenging economic climate, these figures are testament to the efforts of our partners."

Waitrose added that warm weather boosted sales in its most recent trading week to April 27, when they grew 8.4%.

Customers stocked up on suncream to send suncare sales soaring 158%, while ice-cream sales leapt 21%. Salad sales were up 27% and cider sales rose 26%.

The group has been a rare winner amid a stagnant grocery market, with figures from Kantar Worldpanel recently showing its market share hit a record 4.9% in the 12 weeks to mid-April, up from 4.5% a year earlier. The group has 291 shops in the UK and Channel Islands.

It recently sealed a tie-up with cross-Channel train operator Eurostar to supply food and drink in its standard-class buffet carriages.