Countryside chiefs want land earmarked for road development to be included in the proposed South Downs national park, an MP has claimed.

Conservative MP Howard Flight says the changes are a deliberate attempt to spike plans for a bypass at Arundel.

He said there would be significant economic consequences if it was made more difficult to build the bypass.

His comments came after the Countryside Agency voted to make a variation order to the proposed national park boundary, to include land set aside for the road.

Mr Flight, who represents Arundel and South Downs, said: "It has been perceived by the local community as a deliberate attempt to spike the bypass."

The line the road had been expected to follow was excluded from the final national park proposals but there was a rethink after the Government axed the scheme.

The park boundary would be moved south where it crosses the river Arun.

Woodland at Tortington Common and Binsted Wood would also be included if the variation order succeeds.

Jane Cecil, the agency's head of finest countryside, said the land was of national park quality and had been included during early consultations.

She said: "The only reason we withdrew it at the last minute was we felt the bypass was going to be approved. We are not designating land to prevent development."

John Clark, of West Sussex pressure group Protect Our Woodland, said: "A bypass is the last thing most people want. The woodland in that area is more precious than saving a few minutes travelling on a new road."

Mr Flight said the park's boundary line south of Arundel was "particularly odd" and the bypass was urgently needed to reduce congestion on the A27 and cut the number of accidents.

Objections to the variation order will be heard at the public inquiry into the national park proposals, which runs until September.

A ruling on whether the land should be included is expected to be announced when the Environment Secretary makes a final decision on the national park in 2005.