Pre-packed sandwiches may contain as much salt as several bags of crisps, a study suggests.

The health lobby group Cash looked at 140 sandwiches on sale and found more than 40% had over a third of an adult's recommended daily intake.

The "All Day Breakfast" variety were the worst offenders, but cheese and ham as well as chicken salad also featured.

Pret a Manger's All Day Breakfast sandwich contained 3.54g of salt and the Tesco's Finest version contained 3.5g.

The lowest salt sandwiches in the survey were Co-op Healthy Living Tuna and Cucumber and Tesco Healthy Living Chicken Salad, with 0.6g.

The British Sandwich Association was critical of the findings.

"People know that when they buy an All Day Breakfast sandwich it's not the healthiest option" said Simon Hargraves from Pret a Manger

But Ms Butten, one of the health lobby group's nutritionists disagreed.

"One of the easiest way to reduce the salt content would probably be to use a different sort of bread, as that can be a significant factor," said Ms Butten.

Cash singled out Pret a Manger for particular criticism, noting that two of its sandwiches had a very high salt content but that it did not spell out nutritional details on its boxes.

But all customers who were interested could ask at the tills for nutritional information, said Simon Hargraves, commercial director.

"In any event, people know that when they buy an All Day Breakfast sandwich it's not the healthiest option," he said.

"It's just not the kind of sandwich you'd eat all the time."

The government recommends that adults should eat no more than 6g of salt a day. However, the average intake of salt is between 9g and 10g a day.

Some experts estimate that if average consumption was cut to 6g a day it would prevent 70,000 heart attacks and strokes a year.