Hydrogenated vegetable oils are formed as a result of the chemical process of partial hydrogenation, by which liquid oil is turned into solid fat.

These cheap alternatives to other fats, such as butter, are used to improve the texture and increase the shelf lives of many types of processed foods.

But HVOs are also trans fats, which experts say increase 'bad' cholesterol levels in the body, while lowering levels of 'good' cholesterol.

This, in turn, leads to blocked arteries and heart problems.

In its draft Saturated Fat and Energy Intake Programme, published last month, the FSA has pledged to work more closely with manufacturers in a bid to reduce levels of trans fats in food.

The FSA said it would be encouraging manufacturers to reduce levels of trans fats in their products - provided this did not raise saturated fat levels.

Trans fats also occur naturally in red meat and dairy products.