Popular household brands are often no healthier, with manufacturers still a long way from meeting salt reduction targets, Consensus Action on Salt and Health (Cash) said.

The study found 99% of the soups contained more salt per portion than a packet of crisps, a quarter failed to meet the 2010 Food Standards Agency average voluntary targets and just 6% could be labelled green based on the traffic light labelling system.

Cash surveyed 575 ready-to-eat soups from high street chains Eat, Caffe Nero and Pret a Manger as well as branded and own-label varieties from all the major supermarkets.

Some Eat soups contained "astoundingly high" amounts of salt, with 10 products having more than the current daily maximum recommendation of 6g. Eat's largest Bold Thai Green Chicken Curry contained 8.070g of salt per 32oz/907g portion, the same amount as nearly three Big Macs with fries.

Caffe Nero's standard size organic carrot and coriander soup contained 3.6g of salt, more than three-and-a-half times that of the lowest takeaway soup - a Malaysian chicken soup from Pret A Manger at 1.0g per portion.

New Covent Garden Scotch Broth contained the highest amount of salt among the supermarket brands at 2.4g per 300g portion, the equivalent of nearly five packets of crisps. Tideford Organics Moroccan Vegetable contained the lowest amount at 0.44g per 300g portion.

Cash spokeswoman Katharine Jenner said: "People tend to think salt is only in crisps, snacks and ready meals. But this survey shows huge amounts of salt can be hidden in seemingly healthy choices such as soup.

"While there are still soups being manufactured with really high levels of hidden salt it is hard for us to cut down our salt intake to less than 6g of salt a day from the current average of 8.6g a day. "We urge manufacturers to reduce their salt content immediately."

Professor Graham MacGregor, of the Barts and the London School of Medicine and Dentistry and chairman of Cash, said: "The majority of the food industry is slowly taking out the salt from food, including these soups. We commend the progress so far, however they haven't gone far enough if we are to save the maximum number of lives. This survey shows that some companies are not co-operating. The public should boycott these products so we don't have to resort to legislation."