A McDonald’s muffin marketed as a healthier option contains more salt than one of its burgers.

The fast-food chain’s low-fat blueberry muffin has 1.7g of salt – more than in three packets of ready-salted crisps.

The figures come from health campaigners who claim that simple coffee-break snacks are part of the reason the nation is overdosing on salt every day.

Hidden salt in processed foods is said to be fuelling high blood pressure, strokes and heart attacks, leading to thousands of  premature deaths.

A study of coffee-break favourites by Consensus Action on Salt and Health found that while some food chains have made real efforts to cut salt levels, others have apparently failed to act.