PLANS to carve a dual carriageway through a national park will face a legal challenge.

Earlier this month environmental groups reacted with dismay after Highways England announced its choice of route for a new Arundel Bypass.

The £250 million Option 5A will largely skirt the Downs, but still require loss of ancient woodland.

On Thursday the South Downs National Park Authority resolved to begin proceedings for a judicial review to challenge Highways England’s decision.

Highways England’s own environmental experts state that this route will cause significant damage to the National Park’s landscapes.

Margaret Paren, chairwoman of the South Downs National Park Authority, said: “We are not commencing proceedings for a judicial review lightly but we believe that Highways England have not followed the correct procedure, which was to set out, to the same level of detail, all of the options inside and outside the National Park.

“This led to them discounting options outside of the National Park too early in the process, and they have not provided any detail on mitigation and compensation for any of the routes.

“We want to work with Highways England so that they can find a solution to the traffic issues at Arundel that also protects the National Park for future generations, including having discussions around mitigation and compensation measures.”

Paragraph 5.15 of the National Policy Statement on National Networks states that planning permission should be refused for major developments in National Parks except in exceptional circumstances and where it can be demonstrated they are in the public interest.

Consideration of these applications should include an assessment of the cost of, and scope for, developing elsewhere outside the National Park; and opportunities to moderate any detrimental effect on the environment, the landscape and recreational opportunities.

The authority believes the Planning Inspector would not be satisfied Highways England met these considerations.

The route calls for a long stretch of approximately six miles of new dual carriageway, running south of the town and largely skirting the Downs.

From Ford Road, the route continues west passing between the South Downs National Park and ancient Binsted Woods, re-joining the existing A27 at a new junction near Yapton Lane.

Analysis suggests it would draw 62 per cent of the traffic away from Arundel, and reduce traffic through the Downs on the A29 by 33 per cent.