English Heritage's plans for a new Stonehenge visitor centre have been given conditional approval.
The planning permission is conditional on the road improvements
In a letter Secretary of State Ruth Kelly said the scheme could only go ahead once the government had approved the published A303 roads scheme.
English Heritage is now urging the government to give its approval for the road plans "without further delay".
"Failure to do so would miss out on a opportunity to do the right thing for Stonehenge and its visitors," it said.
The published scheme, one of the road options being considered by the government, includes a flyover at Countess Road, a 2.1km bored tunnel, a bypass round Winterbourne Stoke and junction improvements at Longbarrow Crossroads.
Both the published scheme and the new visitor facilities need to be delivered in full if the UK is to fulfil its responsibilities under the World Heritage Convention, English Heritage said.