So, is green tea the answer to our problems?

To its supporters, a cup of green tea offers a worried world a welcome panacea. It protects the heart, cuts the risk of fatal illness, blocks cancer, boosts liver function and provides hope to Alzheimer's victims. It even helped Jade Goody slim down to a size 10.

New research this week went so far as to suggest that it might one day be instrumental in the battle against HIV and Aids. But is it too good to be true?

This spring, from Darjeeling to Zhejiang, armies of pickers are hard at work harvesting the first tender leaves of the tea plant Camellia sinensis to help quench the Western world's growing thirst. Both black tea, the type normally drunk in Britain with milk, and green tea are taken from the same plant. But while black tea is rolled and chopped before being left to oxidise, its green cousin is steamed before drying, imparting the distinctive grassy flavour.

In Britain, sales of green tea have been growing at the rate of 25 per cent a year, fuelled in no small part by the celebrity endorsements of stars such as Gwyneth Paltrow and Jennifer Lopez. But it still accounts for only 2 per cent of the 165 million cups of tea consumed in the United Kingdom each day.

According to Jane Pettigrew, a tea consultant and writer, a number of factors are driving the market steadily upwards. "The health story is a very powerful one but people also like the clean taste which goes very well with the oriental food that many of us like eating nowadays. It is also a good substitute for alcohol and people like the heritage and nostalgia associated with it," she said.

Of course not everyone is convinced by the many health claims. Professor Mike Williamson of Sheffield University, whose laboratory tests this week suggested that epigallocatechin, a component of green tea, could reduce the risk of contracting HIV by coating immune cells, is unconvinced. "There is a lot of rubbish talked about what green tea does and most of it I don't believe," he said. "I think a lot of claims have been exaggerated and the main way they have been exaggerated is that they have used far too much green tea. This can amount to several hundred cups a day - something that presents its own toxicity risk. If you throw enough green tea at something you can show any effect you like," he said.

According to Professor Williamson, whose own study suggested benefits could be gained from drinking two to three cups a day, there is at least one other exciting area of research. Green tea has been found to have the ability to "switch off" stomach cancer cells, something which could one day inform a treatment, he said.

Dr Philip Coan, a physiologist at the University of Cambridge, is if anything even more sceptical. He argues that there has yet to be a sufficiently large study conducted outside the laboratory with the correct controls to establish green tea as a bona fide medicine. "People tend to believe that there are cures for things in simple old remedies but there really is no scientific basis for this," he said.

But according to Cath MacDonald, a nutritionist working for the Tea Council, drinking more than four cups of black or green tea each day offers significant health benefits. Both types of tea contain antioxidants, which destroy free radicals and help protect blood vessels.

"Tea is also a good source of fluid. A lot of people are under the impression that it is dehydrating when it is actually an incredibly good source of fluid and very low in caffeine compared to coffee," she said.