IT is difficult to imagine the British landscape without any oak trees. The English oak, known widely as the king of trees or monarch of the woods, has been part of our countryside for thousands of years and such is its reputation that it was considered sacred by the druids. There are several varieties of oak, such as the sessile, the scarlet, the red, the pin, the Hungarian, the Lucombe and the Turkey, but it is the sturdy English oak with which most of us are familiar.

Now, though, it is under threat. A disease known as phytophthora ramorum has been identified in several garden centres, ranging from West Sussex and Dorset up to Lancashire and Lincolnshire. The disease, caused by the phytophthora microbe which is a fungus-like algae, has been found in viburnums which are a very large group of hardy deciduous and evergreen shrubs.

The affected plants have been imported for sale in garden centres throughout England. The disease, also known as sudden oak death, affects other shrubs including rhododendrons as well as trees like the oak and the beech and it is carried by a fungus which makes the oak bark split and wilt. An affected oak will show a dark red or black sap which oozes from its trunk, and if the bark is removed, the wood beneath will reveal mottled areas of dead and discoloured tissue. Once an oak has been infected, it can die within months.

In California and other parts of America, huge areas of oak trees have been eradicated due to this disease, and it has also been detected in viburnums in Holland and Germany, being first noticed in this country in a viburnum for sale at a garden centre in Chichester. If it affects a viburnum, it begins at a stem and quickly spreads upwards, causing the plant to wilt and collapse very quickly; in rhododendrons, it causes twig and leaf blight with brown or black discolouring and dark brown blotches on the leaves.

I understand that the situation now is that meticulous checks are being made on all viburnums, rhododendrons and sapling oak trees imported from the Continent, while garden centres and nurseries in particular are being asked to carry out meticulous checks of their plant stocks. There is also a ban on the importation of viburnums, rhododendrons, oaks and beech from America, where it seems the disease is almost out of control.

At this stage, it is not certain how the disease spreads, although it is known that the spores can be carried in water or mud, or upon footwear and vehicle tyres, and it is also thought it may be carried on the wind or through the air. The disease is notifiable, which means the Department for Environment, Food and Rural Affairs should be informed if it is suspected, and one recommendation is that if anyone believes they might have a plant suffering from this disease, then their nearest garden centre or nursery should be notified with a view to tests being made.

There is no evidence, at the time of going to press, that trees living in our wild regions have been affected. At the moment, it appears the problem is chiefly associated with imported specimens for sale in garden centres and nurseries, and there are suggestions that our native oak trees may be more resistant than the oaks in North America.

Another concern is whether species of oak other than the common or English oak might be affected, but with memories of the devastation caused by Dutch elm disease, authorities like the Forestry Commission, the Horticultural Trades Association and Defra are not taking any chances. They are making stringent efforts to identify and control the disease, with the necessary ban on certain imports.

It is not just a case of protecting our vitally important oaks, but also our extensive rhododendron gardens.

The oak, which represents something like a third of this country's tree population, is extremely slow growing, which means that its roots spread deeper into the ground, which in turn means it can reach a very great age. It is certainly the longest living of our native trees - it does not produce acorns until it is 60 or 70 years old, and even then it has not reached maturity.

Our countryside is rich with very ancient oaks, often marking historic sites or sometimes giving their name to locations like Oakham, Sevenoaks, Ackworth, Acton, Acklam or Acomb near York. Ack or aack comes from an old Saxon word meaning oak, thus Acton, for example, means oak town and Ackworth means oak farm.

Another curious link is that the druids took their name from the old Celtic word for oak, which was derw. From this, there developed the name of druid, but from it there also derived the name of some rivers, e.g. Derwent.

IF the oak manages to live for a thousand years or more, then the human race is nothing like so long-lived, the "three-score years and ten" still being regarded as normal for most of us. There are exceptions of course, for down the centuries there have been instances of people reaching massive ages and now, it appears, the average age of humans in most countries is steadily increasing.

It is claimed that life expectancy increases by two-and-a-half years in every ten years, and so it is estimated that by the year 2062, many of us can expect to reach the age of 100, Japanese women being the most likely to attain this.

Little more than a century and a half ago (1840) the highest average age for a human being was in Sweden, that age being a mere 45. Now, it is in Japan where the highest average age is 85. Here in England, we are No 18 in that league table, our elderly women averaging 79.9 years of age and our men still averaging little more than three score years and ten, i.e. 75.

The world's authenticated oldest person was Jeanne Calment, a French woman who died in 1997, having attained the incredible age of 122. There are other amazing claims, such as the (male) Japanese silk worm farmer who, in February this year became 112, and the Chinese twin ladies, Kin Narita and Gin Kanie, who in 1999 became the world's oldest twins at the age of 107. Britain's oldest twins, Alice and Nellie Clarke, reached their hundredth birthday in June 2000.

Our newspapers regularly feature astonishing tales of old people, like Nellie Alderson of Richmond, who is taking swimming lessons at the age of 99, Daisy Millar who took her first flight at the age of 103 and Fred Moore, an art student of 107. And there is Janet Thorpe, who lives near Rotherham; she has just started computer lessons at the age of 107 and is now very busy surfing the internet.

In this region, however, there lies the body of a man whose longevity surpasses all those. He was Henry Jenkins, reckoned to be the oldest man in England and even the world, for history suggests he died at the age of 169. His tomb is in the churchyard at Bolton on Swale and is marked by an impressive monument.

Sadly, there is no absolute proof of Henry's age but it is claimed he was born at nearby Ellerton on Swale in 1500, while the parish register at Bolton records his death on December 9, 1670. It is known that he earned a living by thatching houses and although most of his life was spent in agriculture, he became butler to Lord Conyers of Hornby Castle.

Due to his reputed great age, a Mrs Anne Saville decided to check the truth of this and began to test Henry's memory of events. She quizzed him about the kings he remembered, and he referred to Henry VIII; when asked which battle he recalled, he said "Flodden Field", then when pressed to state which king had been present at that battle, he said: "None, he was in France, and the Earl of Surrey was general."

He told Mrs Saville about going to Northallerton at the age of 12 with a horse-load of arrows for use at Flodden and when she checked, Flodden had occurred 152 years earlier, arrows had been used, the Earl of Surrey had been general and Henry had been overseas in Tournay.

From her researches, Mrs Saville became convinced that Henry was the age he claimed and even towards the end of his long life, he took a daily swim in the Swale and walked long distances to go fishing. It must be something in the water!