The efforts of bricks and mortar retailers to build an online presence are being let down by late deliveries, hard to use websites and abysmal levels of customer service, according to a report published today.

The survey, during which mystery shoppers spent 800 hours dealing with 38 leading online retailers, found six of the high street retailers performed "very poorly".

Clothing chain Next came bottom while the others, including Asda, Toys R Us, and Sainsbury, were bad enough to put a shopper off ever going back, the report said.

Two specialist e-tailers, Amazon and Gameplay, "set the standard for the rest".

Dixons, the electrical retailer, was among those criticised. The company's call centre was described as the worst tested. Researchers claim to have called the centre "many times to be greeted only by a busy tone or an unhelpful message saying 'all lines are busy, goodbye'."

Six of 52 items ordered by the testers were delivered late. Dixons was 13 days late, at Next one item was 11 days late, and one of Sainsbury's did not arrive at all.

Marks & Spencer came in for praise, being ranked fourth in the survey, with Homebase the only high street retailer to do better.

The report is published by Javelin Group, a retail consultancy specialising in mail order and e-commerce. "The worst performers were Next and Toys R Us, who failed to meet our expectations across the board," the report said.

• Amazon.co.uk yesterday said it had reached the 3m customer mark. The retailer of books and CDs said the rate of growth in customer numbers was accelerating.

It took Amazon.co.uk 15 months to reach its millionth customer, eight months for 2m and another six months to hit 3m.