A Sussex visitor attraction could change beyond recognition if the public gain free access to it under new right-to-roam legislation.

The owners of Leonardslee, in Lower Beeding, near Horsham, fear they will be forced to spend thousands of pounds in legal fees to prevent more than a quarter of the grounds being opened without charge, robbing them of an income.

Robin Loder, whose family own Leonardslee, says the move would have a "severe impact" on his business, which depends on people paying for admission.

Leonardslee, one of England's last great private gardens, has now become a test case to determine just how far the Government's right to roam legislation should go.

Mr Loder is appealing the Countryside Agency's decision that 65 of the garden's 240 acres should be classified as heathland and therefore be liable for free access.

It is one of 160 appeals made in the South-East, the first area to be mapped, and one of five going to public inquiry before a planning inspector.

But the agency says that, whether Mr Loder wins or loses his case, he will have to pay his own legal fees, which could amount to thousands of pounds.

Leonardslee is one of the UK's largest and most spectacular woodland gardens, enjoyed by an estimated 60,000 visitors each year who must pay for the pleasure.

Under the Countryside and Rights of Way Act 2000, the Government made parks and gardens exempt from the right to roam but the public were to have round-the-clock free access to mountain, moor, heath or common land.

When Mr Loder heard his property was on the agency's web site as an area mapped for the right to roam, he thought it was a mistake.

At first the agency said 150 of its acres were heath but have now scaled it down to 65, which is lightly wooded parkland, grazed by deer and wallabies.

Mr Loder, whose family have owned the gardens for 150 years, says the introduction of 24-hour access with dogs would mean the deer and wallabies would have to be removed and the area would soon revert to scrub.

The Sussex branch for the Council for the Protection of Rural England are backing his argument that Leonardslee should be made an exception as a historic park and garden.

Mr Loder said: "Neither I nor any of our ecologists regard it as heathland, which means to me largely or predominantly heather."

He said he had spent a lot of money tidying up the area since it was badly damaged in the 1987 storm and maintaining its cover of grasses and wild flowers.

Mr Loder has described running Leonardslee as an expensive business but said it survived because it more or less broke even.

He said: "It costs a huge amount - we're talking in the region of £250,000 a year. I'm not a wealthy man and I wouldn't be able to run this garden after 21 years if we didn't more or less break even - or endeavour to."

It could be 2005 before walkers win access rights under the new law.