Researchers who studied almost 1,000 people in five European countries, including Scotland, found the risk of developing the disease increased according to the level of exposure.

Those who had been exposed to low levels of pesticides - such as gardeners - were found to be 1.13 times as likely to have Parkinson's, compared with those who had never been exposed. Professionals, exposed to high levels - such as farmers - were 1.41 times as likely to be affected.

Previous studies have already pinpointed a potential link between the use of pesticides and Parkinson's. But the new study has shown for the first time that the risk of developing the neurodegenerative disease increases according to the level of exposure.

Dr Finlay Dick, a senior lecturer in the department of environmental and occupational medicine at Aberdeen University Medical School, which carried out the research, said the findings were based on a study of 959 people suffering from parkinsonism, including Parkinson's disease, and 1,989 controls in five European countries. "We have been able to show that the higher the exposure, the greater the risk," Dr Dick said.

He said the figures equated to a 9 per cent higher risk factor for low-level exposure and a 39 per cent increased risk for higher exposures.

He stressed, however, that the risk was still "modest", and said: "The typical hobby gardener is perhaps treating their garden with pesticides maybe six times a year for an hour a day. And I don't think our study should change people's use of pesticides.

"Clearly, for people who are using pesticides in their work, there are much more stringent controls on the use of pesticides and they should be using appropriate protective equipment."

Dr Kieran Breen, director of research and development for the Parkinson's Disease Society, said: "The association between pesticides and Parkinson's has been recognised for some time.

"The important finding from this study is confirmation that Parkinson's is not caused by any one factor, but instead a combination of genetic susceptibility and environmental factors."

The study has been published online ahead of it appearing in the journal Occupational and Environmental Medicine.

TIGHTENING THE RULES

PETER Chapman, a Buchan livestock farmer, said: "This possible link between Parkinson's and pesticides is news to me. But I just wonder how much of this is historical.

"The systems in place for farmers spraying their crops are so much higher than they used to be. Spray operators have all to go through training, and be registered and have their machines regularly checked.

"Standards are a lot higher than they were even ten years ago. I would like to hope that what we're doing now is much more professional than what we used to do and that the risk has been considerably reduced from what it might have been.

I know that 20 years ago, you just splashed the stuff around. "