The University of East Anglia team is starting human trials following on from successful lab studies.

Tests on cells and mice showed that a broccoli compound - which humans can also get from Brussels sprouts and cabbage - blocked a key destructive enzyme that damages cartilage.

They are asking 20 patients to eat a daily dose of "super-charged" broccoli.

This special cruciferous vegetable has been bred to be extra rich in nutrients - it is a cross between standard broccoli and a wild relative from Sicily.

Our body takes this glucoraphanin compound and turns it into another, called sulforaphane, which appears to protect the joints.

The volunteers will have two weeks on the diet before going under the knife to have their badly arthritic knees repaired by surgeons.

Dr Rose Davidson and her team will look at the tissue that has been removed to see what impact, if any, the broccoli has had.

She said: "We're asking patients to eat 100g (3.5oz) every day for two weeks. That's a normal, good-sized serving - about a handful - and it's an amount that most people should be happy to eat every day."

While two weeks is highly unlikely to be enough to cause any big change, Dr Davidson hopes it will be enough to offer some evidence that "super" broccoli could benefit humans.

"I can't imagine it would repair or reverse arthritis... but it might be a way to prevent it," she said.

Her team will be looking for proof that sulforaphane has travelled to where it is needed in the joint and that it is causing beneficial changes at the cellular level.

Another 20 knee replacement patients who have not been on the diet will be used as a comparison group.

Prof Alan Silman, of Arthritis Research UK, which is funding Dr Davidson's work, said: "Until now research has failed to show that food or diet can play any part in reducing the progression of osteoarthritis, so if these findings can be replicated in humans, it would be quite a breakthrough.

"We know that exercise and keeping to a healthy weight can improve people's symptoms and reduce the chances of the disease progressing, but this adds another layer in our understanding of how diet could play its part."

The results of Dr Davidson's animal trials are published in the journal Arthritis & Rheumatism.

The special broccoli, known as Beneforte, was developed from publicly funded research at the UK's Institute of Food Research and the John Innes Centre.

More than 8.5 million people in the UK have osteoarthritis, a degenerative disease affecting in particular the hands, feet, spine, hips and knees.