A few days after his 55th birthday Paul Green was standing in his office sorting through papers and dictating letters to his secretary when he noticed that his hands were shaking.

Surprised, he placed the papers on his desk and dropped his arms to his side. The shaking stopped. Relieved, he stretched out his hand to retrieve the documents and the shaking started again. 'Over-tired,' he thought, and resolved to have an early night.

But at breakfast the next morning he found that when he reached for toast with one hand and buttered it with the other, both hands shook slightly. His hand, still when it rested on the table, trembled when he raised his tea cup towards his lips.

By the end of the week he was sitting in his GP's surgery consumed with anxiety after reading in a magazine about Parkinson's disease. His doctor referred him to a neurologist who eventually diagnosed not Parkinson's disease, but a relatively little-known though common condition called essential tremor.

Essential tremor is not nearly as disabling as Parkinson's disease but it is a chronic condition for which there is no cure. Unlike a sufferer from Parkinson's, who can have a resting tremor which disappears on movement, Mr Green shook when he used his muscles.

That was 15 years ago. Over the years his tremor got worse despite treatment with the drugs that sometimes help, such as the beta-blocker propranolol and the anticonvulsant primidone.

Writing became difficult and Mr Green began to dread meals in restaurants or friends' houses when his shaking hands would spill drinks and send food flying. Then suddenly, a few months ago, retired and aged 70, Mr Green finally found a way of overcoming the shakes, albeit temporarily. Cold water.

He heard about the work of a physiologist, Martin Lakie, deputy head of the School of Sport and Exercise Sciences at Birmingham University, who has discovered that lowering body temperature reduces the size of the tremor.

It was a chance finding. He had been looking at tremor in tired muscles after exercise. He simply noticed that the students who took cold showers after working out shook less than those who didn't, and began a new line of research.

He has found that if sufferers place their forearms in tanks filled with cold tap water for five minutes the tremor can be reduced by 50 per cent, the effect lasting for up to 90 minutes.

Mr Green gave it a try and it revolutionised his life: 'If I soak my arms in a hand basin for a few minutes the shaking practically stops. I can shave myself, write letters, sign cheques, have a normal existence until the tremor returns. Without this cooling process I can't drink from a cup or glass without spillage or eat without making a mess; my writing is completely illegible and I can't do anything that needs any fine co- ordinated movement.

'I have heard doctors refer to this condition as 'benign tremor' - it is anything but. This thing can ruin your life.'

Essential tremor runs in the family for about half of all sufferers, and increases with age. But everybody shakes. For most people, most of the time, the tremble in the fingers of a hand and arm outstretched is not, or only barely, perceptible. But we are shaking all the same. Dr Lakie has sensitive equipment that can measure it. In about 20 per cent of 'normal' people the shaking is visible.

So when does a tremor become an essential tremor? That, Dr Lakie says, is a difficult question. As there is no agreed diagnostic test, it is left to the clinical judgement of the doctor carrying out the examination.

In his laboratory he studied tremor in more than 400 'normal' volunteers, men and women of all ages. While the frequency of tremor was much the same for all at between seven and 11 cycles a second, the size of tremor varied enormously.

He uses a miniature meter called an accelerometer. The device, weighing less than 2g, is attached to the tip of the middle finger of an outstretched hand. The subject holds the pose for 80 seconds while the measurement is taken.

'If we exclude a couple of extreme cases who had a tremor 100 times larger than average, the range went up to about 30 times larger,' Dr Lakie says. 'Our findings suggest that essential tremor is very under reported.'

It is difficult to establish the incidence of essential tremor as there

is no generally agreed level of

symptoms. Dr Lakie's definition is a tremor large enough to cause problems with writing, eating or drinking.

But why do we shake? No one knows for certain; there are several theories involving how messages are transmitted. Dr Lakie favours a simple explanation. He believes that when muscles contract in response to nerve impulses they do not do so smoothly. Myriad minute jerks cause a ripple effect which is transmitted along the limb being moved.

Limbs, especially wrists, pick up this ripple effect and resonate with it, normally at about seven or eight cycles a second. Sufferers from essential tremor have an amplified version of this basic resonance. Normally it only affects the arms.

'Essential tremor is particularly noticeable when someone is holding a posture, for instance sitting or standing with an arm outstretched,' says Dr Lakie. 'This sort of tremor is just visible in between 10 and 20 per cent of the population.'

He believes the cooling technique reduces tremor because as the muscles lose heat they lose power and therefore speed. Anyone who has swum in cold water can testify to this. Movement becomes slower - but smoother as a result.

'In the vast majority of cases all that is needed is a bit of reassurance that the worst that will happen is social embarrassment when eating and drinking,' says Dr Lakie.

However, for sufferers determined to get through a restaurant meal or dinner party without having to plunge their arms into a nearby hand basin at regular intervals there is another short-term solution - it seems a stiff drink really does settle the nerves.

Essential tremor sufferers soon discover that alcohol, in moderation, helps settle the shakes. Mr Green used to swear by a nip of whisky - and accept the down-side.

'Alcohol has a very beneficial effect, particularly at a level of around 60mg per 100ml of blood, just below the legal limit for driving,' says Dr Lakie. 'The only problem is that there is a very, very bad rebound effect with a greatly increased tremor when it wears off.'

Mr Green's specialist, Richard Roberts, a consultant neurologist at Dundee Royal Infirmary, says: 'The cooling technique certainly works but it is a bit impractical and this can put people off. If you are out shopping and want to sign a cheque you cannot always find a suitable basin of cold water.

'However, it should not be beyond the ability of someone to design a small portable cooler, like a mini-fridge, which could be carried around.'

Paul Green is a pseudonym.