Oily fish should be eaten at least once a week under healthy eating recommendations.

However campaigners have called farmed salmon the 'couch potato' of fish because it is grown in a confined space and does not swim the same distances as the leaner, less fatty wild fish.

An analysis by the Sunday Times found a classic Pizza Express margherita contains 6.4g of fat per 100g while Sainsbury's Scottish oak smoked salmon made from farmed fish contains 14g of fat per 100g.