Many supposedly healthy soup products from high street chains and supermarkets contain high levels of salt that increase the risk of a stroke or heart attack, a survey warns today.

The health organisation Consensus Action on Salt and Health (Cash) analysed 575 ready-to-eat ranges and identified unhealthy amounts in household name brands including Batchelors and Heinz.

Soup is seen as a healthy light meal or snack alternative, but 99% of those surveyed contain more salt per portion than a packet of crisps.

Adults are advised to eat no more than 6g of salt a day, yet 10 products from EAT, a national chain of 98 sandwich shops, contained more than this. Its "very big" Thai green chicken curry soup has 8.07g in a 907g serving – as much as almost three McDonald's Big Macs and fries.

Across all the 575 products from different brands, although there has been an overall 17% reduction in salt levels since a similar survey three years ago, a quarter of products still fail to meet the Food Standard Agency's 2010 target of 0.6g salt per 100g. High levels of salt are linked to high blood pressure, which increases the risk of heart disease and stroke.

The highest regular-sized high street takeaway soup found was the Caffe Nero organic carrot and coriander at 3.6g per portion, over three and a half times more salty than the lowest, a Malaysian chicken soup from Pret a Manger at 1g.

Batchelors Soupfulls classic beef and vegetable had 3g per 400g portion and Heinz Taste of Home Lancashire lamb hotpot 2.6g per 430g portion.

Katharine Jenner, a Cash nutritionist, said: "This survey shows huge amounts of salt can be hidden in seemingly healthy choices such as soup."

Professor Graham MacGregor, Cash chairman, said: "It is the very high levels of salt that are put in our food that leads to thousands of unnecessary stroke and heart deaths. Furthermore, there is increasing evidence that salt intake is linked to stomach cancer, osteoporosis, obesity and kidney stones and kidney disease."