While eating the recommended five a day still helps reduce the risk of disease, researchers from Imperial College London have said that the highest benefits are seen in people who consume 10 portions.

A portion is 80g - the average apple is 150g and a whole small cauliflower is around 265g.

Consuming 10 portions a day saw a 33% lower risk of stroke, 28% lower risk of cardiovascular disease, 24% reduction in the risk of heart disease and a 13% reduction in the risk of cancer.

It also meant a 31% reduction in the risk of premature death.

But smaller amounts brought benefits. A daily intake of just two-and-a-half portions was associated with a 16% reduction in the risk of heart disease, a 4% lower risk of cancer and a 15% reduction in the risk of premature death.

The research, published in the International Journal of Epidemiology, analyses data from 95 studies on fruit and vegetable intake.

Researchers estimated that if everyone on Earth ate 10 portions daily, then 7.8 million premature deaths could be prevented.

Lead author Dr Dagfinn Aune, from the School of Public Health at Imperial, said: "Fruit and vegetables have been shown to reduce cholesterol levels, blood pressure, and to boost the health of our blood vessels and immune system.

"This may be due to the complex network of nutrients they hold.

"For instance they contain many antioxidants, which may reduce DNA damage, and lead to a reduction in cancer risk.

"It is clear from this work that a high intake of fruit and vegetables holds tremendous health benefits, and we should try to increase their intake in our diet."

The researchers found that leafy greens such as spinach, lettuce and chicory, and cruciferous vegetables such as broccoli, cabbage and cauliflower; apples and pears, citrus fruits and salads may help protect against heart and cardiovascular diseases, stroke and early death.

And green vegetables such as spinach and green beans, yellow vegetables such as carrots and peppers and cruciferous vegetables could reduce the risk of cancer.

Dr Alison Tedstone, chief nutritionist at Public Health England, described the five-a-day target as "the foundation of a healthy balanced diet".

"Whilst consuming more than five portions of fruit and vegetables a day may be desirable, two thirds of adults currently don't consume the recommended minimum of five-a-day.

"Adding pressure to consume more fruit and vegetables creates an unrealistic expectation."

(Additional reporting from IRN)