High street shops are overloading their sandwiches with salt and fat, a survey suggests today.

A sandwich bought in one store may contain twice as much fat, saturated fat or salt as the same flavour snack bought at another shop, research by the consumer group Which? found. For instance, a Morrisons chicken salad sandwich had 11.7g of fat, compared with 6g in the Waitrose version. An egg mayonnaise sandwich sold by Aldi was found to contain 22g of fat, while one bought at Asda contained 10g.

Which? said its findings showed that some chains could make their products healthier. It called for all retailers to use the "traffic light" system of nutritional labelling. Only six currently use the system.

A spokesman for Aldi said: "We offer our customers the opportunity to make an informed choice by providing guideline daily amount labelling as we currently feel this is the best way of keeping our customers informed."

Morrisons said the GDA system gave "a more complete understanding of nutritional values and avoids categorising food as 'good' or 'bad'."