Ministers withdrew their support for the scheme after the costs almost doubled to £470 million.

More than 30,000 vehicles a day pass within 250 yards of the ancient stones on the heavily congested A303 and the A344. The Highways Agency said that traffic was rising by 2 to 3 per cent a year.

Under the agency’s plan, this section of Salisbury Plain would have been returned to traditional, unspoilt chalk downlands grazed by livestock. Visitors would have been able to enjoy the stones without being disturbed by the roar of traffic.

Construction was due to have started this spring and the tunnel would have been completed by 2009. But Stephen Ladyman, the Roads Minister, said yesterday that the estimated cost had risen from £284 million two years ago to £470 million. Tests had shown that the tunnelling would be more complicated than first thought because of weaknesses in the chalk and the high water table.

Mr Ladyman said that a review would be carried out into the scheme but he declined to say when it would reach a conclusion. “Given the scale of the cost increase we have to re-examine whether the scheme still represents value for money and if it remains the best option for delivering the desired improvements.”

The Department for Transport said that last year’s planning inquiry had approved the tunnel. But a spokesman said that it might be cheaper to build a bypass to take the road away from the monument.

Paul Hamblin, the head of transport policy at the Campaign to Protect Rural England, voiced concern that the Government could decide to cut costs by using more environmentally damaging tunnelling techniques. The original plan was to cut a groove in the landscape and put a cover over it, but in 2002 the Government acknowledged that that could damage ancient relics around the monument and decided to bore a tunnel instead.

The section of the A303 running past Stonehenge is one of the few remaining singlecarriageway sections of the popular holiday route to Devon and Cornwall. The tunnel scheme would have included upgrading the section to a dual carriageway. The Save Stonehenge! group welcomed the review. It admitted that the scheme would have benefited the stone circle but said that other parts of the 6,500-acre World Heritage site would have been damaged.

It objected to the digging of four-lane cuttings down to the tunnel and the building of a giant interchange to the west of the stones. A spokesman said: “This scheme has become a white elephant — a half-billion-pound monster that would stampede through one of the world’s best-loved landscapes, wreaking havoc and destruction — and must be scrapped immediately. This was always a quick and dirty motorway scheme pretending to be an archaeological improvement.”

English Heritage, which manages Stonehenge, said that the scheme remained the best option for “realising the vision of reuniting Stonehenge with its landscape and improving the experience for visitors”.

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