Research carried out by the government-funded Food Standards Agency (FSA) found that in a single serving, a slice of the 77 soups tested contained as much as half of the 6g recommended maximum daily intake for adults.
Many soups contained as much as a third of the advised intake, added the FSA, which recently launched a nationwide campaign to slash salt levels in consumer diets.
Gill Fine, director of consumer choice and dietary health, at the FSA said: "We welcome the commitment that some manufacturers and retailers have made to reduce salt content in soups but the fact that such a popular and convenient food can provide more than a third of the daily salt limit shows that continued effort in this area is still needed.
Food makers use salt extensively in food formulations for the most part to improve flavour and preserve, but also for texture and to balance specific processes, to control yeast growth and fermentation rate in bread, or to inhibit clouding of vinegar in pickled products.
The FSA findings square against recent targets set by the UK's €99.58bn food and drink industry and the FSA to cut sodium content in a range of products. Members of the Food and Drink Federation's Project Neptune agreed to make a 10 per cent reduction in the levels of salt in soups (tinned, packet and instant) and sauces each year from 2003 to 2005. Project Neptune has just announced that it achieved a 20 per cent cut in sauces and a 6 per cent reduction in soups in 2003.
Condemned for contributing to the worsening health problems in the population, consumer groups have come down hard on the food manufacturers pushing them to reduce the salt used in food recipes.
Eating too much salt is a significant risk factor in developing high blood pressure, itself a cause or contributing factor in the rising incidence of heart disease.
Recent figures from the FSA claim that every day at least 26 million people eat more than the recommended daily limit of 6g of salt. Men are eating the most with a daily average of 11.0g of salt while women consume an average of 8.1g a day.
The latest soup survey looked at the salt content in 77 fresh/chilled, canned and packet soups, including varieties of both the top sellers in each category and a range of retailers' own brands. It showed that not only is there wide variation within each category but also within each flavour.
The dried soup category showed the largest range (1.2g to 2.9g) of salt content per serving, while two brands of canned mushroom soup contained twice the amount of salt as another canned mushroom brand. No brand was consistently high or low in salt.
For making comparisons, a standard portion size of 200g was used for all the soups surveyed that covered vegetable, tomato, chicken and beef/oxtail canned soup flavours.
Sommerfield cream of tomato with 42 per cent of daily salt intake had the highest salt content in canned/ambient soups, with Asda cream of mushroom at 1g, (17 per cent), the lowest content.
In the fresh/chilled category Tesco's fresh minestrone soup at 2g, or 33 per cent of recommended daily intake, came out as the highest, and the lowest, New Covent Garden Company fresh chicken soup with 1.0g, or 17 per cent.