Cooking with vegetable oil releases toxic chemicals linked to cancer and even the degeneration of the brain, according to experts.

Lard, butter, coconut and olive oil are all better dietary choices, leading scientists have said - in advice which directly contradicts the NHS.

When heated, corn, sunflower, palm and soya bean oils - often called "vegetable" oils - release chemicals called aldehydes which have been linked to various cancers and neurogenerative diseases such as Alzheimer's.

Martin Grootveld, a professor of bioanalytical chemistry and chemical pathology at DeMontfort University,said that a meal fried in vegetable oil such as fish and chips contains 100 to 200 times more aldehydes than the daily limit set by the World Health Organisation (WHO), according to the Daily Telegraph.

Using butter, olive and lard in the frying pan, however, was found to produce much lower levels of aldehydes - with coconut oil coming out as healthiest.

Scientists said meal fried in vegetable oil such as fish and chips contains 100 to 200 times more aldehydes than the daily limit set by the World Health Organisation (WHO).

Yet the NHS has long warned against cooking with butter and lard. The NHS choices website advises:

"Try to cut down on foods that are high in saturated fat and have smaller amounts of foods that are rich in unsaturated fat instead.

"For a healthy choice, use just a small amount of vegetable oil or reduced fat spread instead of butter, lard or ghee."

Yet vegetable oil has been linked to heart disease, cancer, inflammation, rising blood pressure and mental health.

And the omega 6 fatty acids present in vegetable oils are pushing out the important omega 3 fatty acids that keep the brain healthy, according to Professor John Stein, emeritus professor of neuroscience at Oxford University.

"If you eat too much corn oil or sunflower oil, the brain is absorbing too much omega 6, and that effectively forces out omega 3,” Prof Stein said according to the Daily Telegraph.

“I believe the lack of omega 3 is a powerful contributory factor to such problems as increasing mental health issues and other problems such as dyslexia.”

The issue had not received enough attention by health organisations or the food industry, experts added.