Huge and gnarled, with long trailing branches heavy with bunches of a small reddish fruit, the magnificent old tree standing in front of us in a neglected orchard on a south Wales farm is probably the last of its kind, its name and variety long forgotten.

Huge and gnarled, with long trailing branches heavy with bunches of a small reddish fruit, the magnificent old tree standing in front of us in a neglected orchard on a south Wales farm is probably the last of its kind, its name and variety long forgotten.

Dave Matthews reaches up and selects a fruit. He takes a bite, grimaces and spits his mouthful onto the ground. 'Wonderful,' he says.

It is a perry pear, used to make one of the country's oldest and most traditional drinks, a sister to cider and the sparkling version of which was once dubbed by Napoleon as the 'champagne of Britain'.

Explaining his grimace, he says: 'When you try and eat it, the taste is pretty awful, full of and acids. But press the juice out and those tannins and acids turn into something fantastic. And in this case you are tasting a drink that is unique and possibly hasn't been tasted for many years, perhaps for more than a century.''

The local tradition of local perry making and drinking, never practiced as extensively as cider, has almost died out. Dave is on a mission to revive it and to preserve the ancient and unique trees and orchards from which it was once made.

Since pear trees reputedly take '100 years to mature, 100 years to fruit and 100 years to die'' this tree, growing at the rear of a somewhat ramshackle farmyard in the countryside south of Newport in south Wales, could be more than two centuries old. And its fruit bears no resemblance to any of the other recorded perry pear varieties, of which there are at least 60; nor do any of the locals around here recall the variety.

Dave called the 35 gallons of perry he has made from this tree the Little Cross Huff Cap, after the name of the farm and generic term for pears with such an elliptical shape as this one; the three full bottles he leaves at the farmhouse in payment for harvesting the pears are akin to a single malt whisky or wine from one vineyard - a one-off taste.

According to Dave, it was probably planted as part of a small orchard for the farm, providing a mix of pears and apples for drinking, eating and cooking. Perry can be made from one variety of pear, while cider requires a blend of different apples. "This was simply the tree the farm would have used in the past to make their own drink," he says. "This one has a beautiful pineappley flavour to it. I'd just love to be able make more. But we simply don't know whether any more of these trees survive. It was a local variety, distinctive to this area. For all we know this is the last one of its kind."

Over the past few years, working in his spare time, the biology teacher from an inner-city Cardiff secondary school has travelled the back roads and lanes of the Gwent levels south of Newport and up into the hills and valleys of Monmouthshire seeking out such sites as Little Cross. Locals have helped him find trees and identify varieties. As well as finding nameless pears like the Little Cross one, he has rediscovered others like the Burgundy and Potato varieties, once believed to have become extinct.

Until the practice died out in the 1950s, the area was thick with orchards and had a rich, indigenous cider and perry culture, akin to its neighbours over the border in Gloucestershire, Herefordshire and Worcestershire.

Dave now has more than 30 sites on his records, ranging from isolated single trees to whole orchards, about a quarter of which are perry pears, the remainder apples. "These are mere fragments of what once existed; less than one per cent in my view,'' he says. "People generally have been very helpful - you are bringing back memories of their past. I had one women in tears remembering her late husband's orchard. To me it is about preserving the genetic heritage of our countryside.''

Over the past couple of weeks he has been touring the sites to assess the fruit levels for the coming harvest, his car boot filled with cider and perry to repay the orchard owners; some prefer just cash.

Through this process, he is encouraging landowners, farmers and smallholders to keep their orchards rather than, as is commonly the case, get rid of them. It is an urgent task, needed to halt a dramatic decline. According to DEFRA, over the past five years more than 10 per cent of all British orchards have been lost, while the number of registered apple and pear growers have dropped from 1,500 in 1987 to just 500. This is occurring because farmers are encouraged to plough them up to plant subsidised crops, and supermarkets which now dominate prefer to buy regular mass-produced crops from overseas, without any of the blemishes or irregularities that occur in smaller orchards.

Fizzy, commercially marketed cider and drinks like 'Babycham' or 'Farmhouse Scrumpy,' bear no resemblance to perries. Mostly, perries are still drinks, fermented in barrels from the pressed juice, with an alcohol level around that of wine and made to be drunk by the glass with food rather than by the pint. The sparkling versions are made by either adding yeast and sugars.

From Little Cross, Dave heads for the farm of Kath Johnson, 63, whose family have worked the land on the Gwent levels for generations. Dogs and grandchildren swarm around her flower-bedecked farmyard and ducks swim in the pond. She produces an old photograph - she thinks from the 1940s - of a horse-drawn travelling cider press visiting the farm to press its apples and pears. "People stopped doing all this years ago. If Dave didn't come here, then all the apples and pears would go to waste.''

She waves us down to the orchard, where there is another nameless perry pear tree, with a curious mushroom shape. Dave has named this perry Little Owl, in honour of the baby screech owl that flew from its branches the first time he came. It needs, he warns Mrs Johnston, just a little time longer in the bottle for the tannins to settle. But the bottles from two other trees she told him about - a well-known variety called Blakeney Red - are ready for drinking.

Later, we travel up the Usk valley to the farm of John Evans, one of few farmers to actually begin planting new apple and pear trees. He makes cider and sells the pears to Dave. In a stone vault next to the farmhouse, we sample his clear, golden cider, drawn straight from a barrel that formerly held rum. It is remarkable, closer to an apple wine or a full-bodied Australian Chardonnay than cider, dry but full of fruit flavour.

He leads us up the valley behind his farm to a tranquil spot where several huge old apple trees cling to a steep slope; they need care and attention.

John explains that this is the land of a neighbour, who bought the house, but now doesn't want the land. Changes in rural economies mean there is little to be gained from keeping it; the fate of the trees is therefore uncertain. But the destiny of some others has been decided, says John sadly: "There was a lovely row of mature pear trees over there, but someone cut them down."