The findings, reported across the national media, provide some fuel for the use of low-fat ingredients in sandwiches.
The research, carried out by diet and fitness website DailyDietTracker.co.uk, analysed the contents of almost 50 sandwiches available in well-known retailers.
The highest content was found in a cheese and onion sandwich from Marks & Spencer, with 41.9g of fat per pack. It contains red Leicester and medium Cheddar cheese, mayonnaise and salad cream.
The Food Standards Agency suggests no more than 35 per cent of the daily energy intake for an average adult should come from fat.This works out at around 86g of fat for an average man and 61g for an average women.
More that 2.4 billion sandwiches are bought in Britain every year, in a market worth £3.5 billion in sales.
Cheese-based sandwiches featured prominently in the list of the 10 fattiest sandwiches in the survey. In second place was a cheese and onion from supermarket chain Asda with 41g of fat, followed by a red Leicester and Spanish red onion variety from bakery chain Greggs, with 37g of fat.
Sandwiches from Tesco, Sainsbury's and Pret-a-Manger also made the top 10.
The companies responsible for making the fattiest sandwiches on sale said, in their defence, that they also offer a range of low-fat sandwiches and provide customers with nutritional information to enable them to make a choice.