A major hurdle to the full dualling of the A11 was lifted last week after it emerged that two conservation bodies had withdrawn their objections.A rare migrant bird had threatened to stall the upgrade of the last single carriageway stretch of the road between Thetford and Barton Mills after the RSPB and Natural England raised concerns about the impact on the protected stone curlew.

A major hurdle to the full dualling of the A11 was lifted last week after it emerged that two conservation bodies had withdrawn their objections.

A rare migrant bird had threatened to stall the upgrade of the last single carriageway stretch of the road between Thetford and Barton Mills after the RSPB and Natural England raised concerns about the impact on the protected stone curlew.

But the two organisations confirmed on Friday that they had withdrawn their opposition to the Highways Agency scheme - just five days before a public inquiry is due to start. The news has slashed the estimated length of the inquiry, which is set to open on Tuesday, from eight days to six.

Fears had been raised about the affect of the nine-mile road scheme, which would bypass Elveden village, on the nationally important stone curlew, which thrives in heathland areas in the spring and summer. An estimated two-thirds of the 340 breeding pairs in the UK live in the Brecks.

But John Sharpe, conservation manager for the RSPB in eastern England, said following “constructive discussions” with the Highways Agency, the charity was in agreement with the mitigation measures proposed for the stone curlew population and other wildlife.

“The RSPB has always recognised the significance of this road proposal to the region. Our primary goal has been to ensure that protection of Breckland's natural heritage is a central part of delivering the road,” he said.

Shaun Thomas, Natural England's east of England director, added: “Natural England is delighted that we have been able to reach agreement with the Highways Agency on a suitable package of measures that will protect the valuable wildlife in the area at the same time as allowing the improvements to the A11 to go ahead.”

The bodies have agreed that a total of almost 190ha of land should be set aside for the creation of new habitats for stone curlews, woodlark, and nightjar, which would be displaced by the creation of the dual carriageway.

South West Norfolk MP Christopher Fraser said: “This is good news for Thetford and for Norfolk as a whole, but I make no apology for repeating my message that everything must be done to ensure that construction can start as planned next year.”

There now appears to be just six objectors to the dualling scheme, which is estimated to cost �135m, and is scheduled to start this time next year. Concerns about the impact of increased traffic on the Fiveways roundabout at Barton Mills and issues around the B1112 junction still remain.

Opposition from the Suffolk Federation of Byway and Bridleway Groups has also been withdrawn after an underpass for horse riders, cyclists, and walkers was included in the plans near the Elveden Monument.

Ann Steward, cabinet member for economic development at Norfolk County Council, said she hoped the news would lead to a swift and positive conclusion to the public inquiry.

“This is a significant and positive development which removes another obstacle standing in the way of this much-needed scheme which is vital for the good of the Norfolk economy,” she said.