"Higher temperatures and climate change is adding to people's woes still further. This really is the first time there has been a medical, or consumer angle, to the climate change story," a spokesman for the Woodland Trust told Reuters yesterday.

"We've all heard about its impact on species but this is the first time that we will actually see an impact on people as well," he added.

The Woodland Trust, Britain's leading woodland conservation charity, sponsors the yearly phenological survey by 18,000 recorders across the country.

Volunteers jot down the first signs of spring, such as the flowering of grasses, blooming of flowers and trees and arrival of certain birds and butterflies, which is helping the trust build a database to make predictions about seasonal changes.

"What we are seeing is a trend to a much earlier spring. Basically what is happening is that winter is being squeezed in the middle. Autumns are lasting for much longer and springs are arriving earlier," the trust spokesman added.

About 25 percent of the population suffer from hayfever, which is caused by a reaction in the body to pollen released by plants into the air.

Most cases of hayfever, or allergic rhinitis, are triggered by grass pollen. About 20 percent of sufferers are allergic to birch pollen. The first medically described case of hayfever was recorded in 1819 but the cause was not pinpointed until 1873, according to the trust.

"Last year the grass pollen season was exceptionally long because it was wet and warm. The season extended into August, instead of ending in July. Generally, hayfever is affecting more and more people," said Professor Jean Emberlin of the National Pollen Research Unit.

According to the phenology statistics certain grasses flowered between nine to 13 days earlier last year than the year before.

Emberlin said the survey gives experts information about flowering times in advance of pollen release which will help to improve forecasting of the start of the pollen season. (Reporting by Patricia Reaney; editing by Steve Addison; Reuters Messaging: patricia.reaney.reuters.com@reuters.net).