Sainsbury's insisted this week that the second website fault in a month had had no impact on sales and was solved within 24 hours.

It was a case of déjà vu for customers logging on last Friday, when they were greeted with a temporary homepage after the permanent one went offline.

However customers were still able to order their weekly shopping by accessing the food site direct and a Sainsbury's spokeswoman said it was a "totally different" problem to the major meltdown it suffered last month.

It might have been due to a power failure, she said. "It lasted just 24 hours and there was a temporary homepage up in an hour."

A technical problem on 17 June left thousands of customers unable to order food online for over 48 hours.

The breakdown prompted rivals to cash in by offering discounts to disappointed Sainsbury's shoppers. At the time computer expert Andy Testa said the problem was likely to have been caused by Sainsbury's upgrading its software without thoroughly testing it first.