Major multiples have been accused of extending Sunday hours by the back door through browsing.

The blast came as the government announced that it would not be relaxing current Sunday trading laws in England and Wales.

The Federation of Wholesale Distributors said that the practice, where stores open earlier allowing shoppers to fill trolleys, but not pay for goods until the official store opening time, was "a back-door trick".

The Forum of Private Business said it was "an example of how supermarkets try to bend the rules if they have an opportunity".

Morrisons is the latest retailer to introduce browsing periods. A spokesman said: "Around 50 of our stores are open about 30 minutes earlier on a Sunday for browsing. We have done this for the convenience of our customers."

Tesco confirmed that the company offered Sunday browsing, but said it was at the discretion of each store manager. Asda said it had been allowing Sunday browsing for some time. "It helps ease the pressure on our busiest day." Sainsbury also offers Sunday browsing, again at the store manager's discretion.

Pro-Sunday trading lobby group Deregulate said the growth of Sunday browsing was a "clear indication that consumers want more time to shop on a Sunday."

Trade and industry secretary Alistair Darling confirmed this week that the government would not be changing the current Sunday trading laws in England and Wales.