Ancient chalk grasslands dating back 2,000 years are under threat according to conservationists.

The Sussex Downs Conservation Board has written to the Government asking for pressure to be put on a farmer to remove a 100sqm pen on chalk grassland at Hoddern Farm, near Peacehaven.

Chalk grassland is a rare protected habitat, thought to contain as many species of plant, insect and animal per square metre as a rainforest. It is only found in north western Europe and covers three per cent of the South Downs.

Countryside manager Phil Belden said: "We are very concerned about the potential loss of a piece of chalk grassland but it is not too late. The pheasant pen should be moved to a less sensitive location.

"If it is left there it will destroy the habitat."

The land is protected by the Government which provides grants for farmers who look after such habitats under the environmentally sensitive area (ESA) scheme.

It is also part of a designated area of outstanding natural beauty.

Mr Belden said: "Because he's in the ESA scheme he's being paid to maintain the chalk grassland. If he's breeding pheasants on the land instead there is an issue there.

"In the 21st Century we cannot afford to lose any more of these incredibly rare habitats. We are down to three per cent of the Downs and we need to build on that, not lose more."

Conservationist Dave Bangs, of Ewhurst Road, Brighton, said he would be willing to help the farmer move the pen to another location away from the chalk grassland. He said: "I once counted 79 species within half an hour at the site, it is teeming with life and it would be a disaster to lose it.

"I've seen the dark green fritillary butterfly there, which is a litmus test of the quality of a site. You rarely see them. This is the last chalk grassland site along the Ouse Valley between Piddinghoe and Newhaven.

"I am worried that a chalk grassland that has possibly been there for two millennia is about to be destroyed."

Farmer John Carr was unavailable for comment.