A £47m road through the valley where William the Conqueror struck his first camp outside Hastings was approved by the transport secretary, Alistair Darling, yesterday, to the dismay of environmentalists.

The Hastings-to-Bexhill link passes through the Combe Haven marshes, where the Norman invaders spent the night after landing in Pevensey Bay.

Mr Darling accepted that the road was crucial in regenerating Hastings and relieving congestion on the existing seafront route.

His decision came three days after he risked the wrath of the motoring lobby by turning down a £340m plan for a dual carriageway to the West Country cutting through the Blackdown Hills on the Devon and Somerset border.

Steve Hounsham, a spokesman for the environmental pressure group Transport 2000, said: "Where is the logic in this?

"Putting these two decisions together, there doesn't seem to be any overall sense of direction on roads from the government."

East Sussex councillors originally wanted a six-lane bypass of Hastings. Critics said this was part of a grand plan to create a south coast "superhighway" from Kent to Devon. It was blocked by Mr Darling's predecessor, Stephen Byers, on environmental grounds three years ago.

Friends of the Earth argued that the latest proposals could produce a bypass "by stealth" by piecemeal roadbuilding over a period of years. But a Department for Transport spokesman pointed out that the link road was a single carriageway route which had been re-routed to skirt around an area of special scientific interest.

Hastings, population 85,000, is not linked to any dual carriageway road.