The new South Downs national park should be extended into the Channel, say countryside campaigners.

The pro-national park South Downs Campaign has criticised proposed park boundaries which stop where the Downs meets the sea between Seaford and Eastbourne.

Campaigners say a marine conservation area should be included and would help preserve the coastline between Seaford Head and Beachy Head, already protected as heritage coast.

They want the boundaries up to five kilometres into the Channel and if they get their way it would be the first time a national park in England and Wales has been extended offshore.

Campaign chairman Robin Crane said the area contained important shipwrecks and geological sites and including it in the park would be important for wildlife and attractive to sport divers.

He said: "The sea off the Seven Sisters heritage coastline is part of its setting as well as having important ecological and archaeological interest.

"It would benefit from being included as well as potentially having educational and research advantages."

The comments form the group's first response to boundary proposals drawn-up by the Countryside Agency, the body in charge of creating the park.

The proposals are also criticised for not including river valleys in the approaches to the Downs, or downland outside the existing area of outstanding natural beauty, such as between Whitehawk Hill and Newhaven.

Mr Crane said: "There are some important areas of the Adur and Ouse valleys which should be included, while a more consistent approach needs to be taken, especially north of the Downs, to protect the views across the Weald and to provide gateways to the national park."

The agency published its proposals in March and they will form the basis of a consultation on formal boundaries starting in September.

The agency said the proposals did not represent a fixed line and the formal designation order, including the final boundary, was not expected until mid-2002.

The park itself is unlikely to be created before 2003.