Planning bosses want to rethink a series of tunnels costing £250 million proposed to carry traffic under protected Sussex countryside.

Regional planners fear building tunnels under environmentally-sensitive sites to take the A27 around Worthing and Lancing and under parts of the South Downs would be too expensive.

The South-East England Regional Assembly's planning committee said more work was needed to examine the cost effectiveness of tunnelling.

A recently published transport blueprint for Sussex proposed three short tunnels to avoid building on the South Downs, which has acted as a brake on bypassing Worthing and Lancing since the project was mooted in the Sixties.

Committee member Bob Page said abandoning the tunnels would inevitably mean an above-ground route across protected downland.

He said: "The road options are damaging. Four of the road sections go through the area of outstanding natural beauty and the proposed national park."

The tunnels, which would follow the route of the existing A27, are among a series of road schemes in the South Coast Multi-Modal Study, intended to guide transport policy in Sussex for the next 30 years.

A new bypass around Arundel and a Bexhill to Hastings link road are also included in the document.

Martin Tugwell, head of regional transport planning, said the committee had accepted the principle of building bypasses at Worthing and Lancing but wanted to make sure they would be value for money.

He said: "What we are talking about is the need for future work to be undertaken to make sure we have the best and most practical option."

Among the study's other proposals were congestion charging in major centres such as Brighton and Hove, a levy on workplace parking, park-and-ride schemes and improved rail and bus services.

The full regional assembly is to meet next month to make its recommendations on the document.