Marks & Spencer is bucking the trend for smaller pack sizes by adding extra filling to its sandwiches without increasing the price.

Its prawn mayo sandwich has been bulked up the most and now contains 40% more prawns, followed by the chicken salad sandwich, which has 35% more chicken. Other changes include 30% more cheese in the ham, cheese and pickle sandwich, 20% extra chicken in the chicken & bacon sandwich and 20% more ­bacon in the BLT.

The new sandwiches are being rolled out across all its food stores and their launch is being supported by an advertising campaign in the national press.