Bodiam Castle in East Sussex is among the Trust's attractions

The Trust said membership had soared over the past two decades, reflecting an increase in public enthusiasm for heritage and the environment.

Its joining rate was now higher than the country's birth rate and still getting faster, it said.

The Trust holds its AGM on Saturday, in which members will vote on issues including GM crops on Trust land.

Other issues to be voted on include the development of housing in derelict land on the Cliveden Estate.

Pay-for-entry properties

The 1m member barrier was passed in May 1981 and by October 1990 there were 2m members, the Trust said.

Membership had increased by 20% in the past two years alone, from 2.8m to 3.3m, and the latest figures show the Trust's growth continues to accelerate.

At the end of September 2003, the Trust had welcomed 12.8m visitors to pay-for-entry properties, compared with 10,5m at the same time last year - up 22%.

Thousands of extra visitors have flocked to Hardwick Hall

The Trust said it was estimated 50m people a year visited the open air sites.

Several properties exceeded their visitor number expectations, including Sudbury Hall in Derbyshire, which had 57,000 more visitors than last year.

Bodiam Castle in East Sussex attracted an extra 30,000 visitors, while Hardwick Hall in Derbyshire had 25,000 more.

Passionate interest

NT chairman William Proby said: "These remarkable figures are proof of the robust good health of the Trust.

"But they also reflect the passionate, growing interest of British people in heritage and the natural environment.