Dairylea Light cheese slices, iconic school lunch-box food in Britain, contained 2.8g of salt per 100g, according to campaigns group Consensus Action on Salt and Health (Cash). It said that compared to 2.5g of salt per 100g in the Atlantic Ocean.
The group added that nearly three quarters of the cheeses it examined did not show salt levels per serving on their packs, making it hard for consumers to monitor their intake.
The Cash survey, which sampled around 175 cheeses, again puts the spotlight on cheese producers in the UK's government-led campaign to cut consumers' salt intake.
Eating too much salt is widely associated with increased risk of heart disease. A study by the UK Food Standards Agency (FSA) released last autumn found British men were eating an average of 11g per day, with women on 8g per day. The recommended daily maximum is 6g.
Most of this salt intake comes from processed food, including processed cheeses like Dairylea.
Kraft Foods, the owners of Dairylea, said in a statement it was working actively with the FSA to cut salt in its cheese. "Average salt content across the Dairylea range was reduced by 30 per cent between 2002 and 2004," it said.
Reducing salt is a tricky business for food firms, however. Kraft said: "Salt is an essential part of the cheese-making process and levels vary between different types of cheese. Salt levels in Dairylea are now at the limits of what can be achieved within current technical, food safety and consumer acceptance constraints."
Dairylea Light cheese slices, like those examined by Cash, already lie within the FSA's new salt targets for the dairy industry. The agency set the maximum level for salt in processed cheese at 2.9 per 100g earlier this year.
It also set a 2g per 100g salt target for cheese spreads, although backed down from putting a limit on blue cheese, in the wake of industry lobbying.
The agency had wanted to set a limit of 1.9g, but the move annoyed Stilton producers, who said their cheese was made to a specific recipe to ensure its protected origin status in the EU. Stilton typically contains 2g of salt per 100g, compared to Danish Blue on 3.1g and France's Roquefort on 4g.
Cash criticised the FSA earlier this year for caving in to industry pressure on salt reduction targets for several foods, jeopardising the agency's goal of cutting average consumption to 6g per day by 2010.