The consumer and pressure group Consensus Action on Salt and Health (CASH) say bread is the largest source of salt in the British diet and excessive consumption can lead to increased blood pressure and a greater risk of heart attack.

In a study which condemns many supermarket brands of bread, the group has called on British shoppers to boycott breads with the highest levels of salt.

In a survey of 138 widely available loaves, researchers for the group found that more than one in three contained salt levels above the Government's target of 1.1g per 100g.

The highest level was found in Morrison's Best Farmhouse Malted Bread, which had a level of 1.5g per 100g or 0.7g per slice, four slices of which would put a child of six over the maximum daily recommended salt intake of 3g. while nine slices would take someone over the adult threshold of 6g.

The researchers found the second highest salt levels in several Asda loaves, which had a level of 0.6g per slice and a total of 15 out of 18 Warburton products had a salt content higher than the Government's target, while all of the Sainsbury's and Waitrose breads surveyed were below.

A spokesman for the British Heart Foundation (BHF) says research shows that despite some progress in reducing salt levels in bread, there remains wide variations in how much is contained across similar products.

The BHF says people who are at risk of heart disease caused by high blood pressure need to reduce salt in their diets, and need to be able to quickly and accurately choose lower salt options when shopping.

The charity is calling for the industry to adopt the traffic light labelling system developed by the Food Standards Agency which uses red, amber and green logos to tell shoppers whether products are high, medium or low in salt, sugar and fat.

According to the Federation of Bakers their members have made huge strides in reducing salt levels since 2005 and the industry has agreed that bakers have until 2010 to reach the target of 1.1g of salt per 100g.

CASH says reducing the amount of salt in sliced bread could save at least 7,000 lives a year.

Professor Graham MacGregor, the chairman of CASH and a professor of cardiovascular medicine, says bread is the largest source of salt in the UK diet and if the salt content of all the bread on sale in the UK was that of the lowest levels found in this survey, the average population daily intake would be cut by around 1g.

MacGregor says research has shown that a population cut of 1g of salt per day would equate to 7,000 lives saved each year from strokes and heart attacks due to the drop in blood pressure that would occur.