The printed labels on pre-packed sandwiches must be easier for consumers to understand, experts have insisted.
According to Which?, many coffee shops, supermarkets and other retailers already use a very simple traffic light-based system to show nutritional information on these items.
However, the consumer group said this is not being used across the board, which means some people find it difficult to identify the healthiest options.
Richard Lloyd, executive director of Which?, commented: "With obesity levels reaching epidemic proportions, it's more important than ever that consumers know exactly what they're eating."
The organisation argued that if the same labelling system is not in place at all retailers, the healthiest products will not always be obvious to shoppers.
This could be important as Which? found that the salt and fat content of pre-packed sandwiches varied considerably between all the companies it examined.
A consultation on introducing a clearer and more consistent food labelling system was launched this week by the government.
Denny Bros Ltd, 18 May 2012