News that a bid to get Brunel's most-admired engineering feat listed as a World Heritage Site has failed has met with bitter dismay from campaigners.

The Great Western Railway, stretching from London Paddington to Bristol, was one of 11 important chapters in the country's industrial history to make it onto an elite watchlist of 25 potential sites to be inscribed with the lofty status a decade ago.

This would mean the route, nicknamed "God's Wonderful Railway" had the same standing as sites like the Taj Mahal, the Great Wall of China and Stonehenge.

At a conference in Bristol in 2006, English Heritage deemed the line and its array of tunnels, cuttings, bridges and stations, a "breathtaking" monument to British endeavour and one that should achieve worldwide recognition.

But the organisation that hands out the accolade, UNESCO, wants more sites from developing countries and a slowdown on European bids.

Now the Government has launched a consultation that could lead to a complete block on sites that feature on the 'Tentative List', which includes the railway, making it through to the next stage of the process.

The news has angered members of Bath Heritage Watchdog and railway enthusiasts, who are keen to see selected parts of the line, originally described by English Heritage as a "string of pearls, with valuable beads nestled between the jewels", preserved with the highest-possible safeguards for generations to come.

They have launched a campaign and are urging all fans of the railway to lobby English Heritage and the Department for Culture, Media and Sport and force a rethink,

Spokesman Jim Warren said: "Network Rail obviously will look after the site but if it achieved WHS status, aberrations like the proposed fly-over by the line at Reading would not be allowed to go forward.

"What English Heritage originally proposed doing was getting eight sites, or 'pearls' along the route inscribed with this status – places like Box Tunnel near Bath, which at the time of its construction was the longest railway tunnel in the world, and Bristol Temple Meads Station, now the oldest surviving railway terminus in the world.

"The 'beads' include, among others, the Great Western Railway Centre at Didcot and the ornamental viaduct and massive embankment through Chippenham.

"Obviously we are particularly concerned with the railway as it stretches through Bath, but there must be other groups like us along the line just as worried at this news."

The group recently carried out a survey of the many Brunel railway assets in Bath, which include the Grade II-listed Sydney Gardens embankment and bridges,

Bath Spa Station and station ramps, St James' Railway Bridge, the railway bridge and arches along the Lower Bristol Road and the station house and arches in Twerton, are believed to be the only example of Brunel's domestic architecture in the country.

Mr Warren said: "We were appalled to see the current state of repair many of them were in, though it must be emphasised that there is no current risk to the safety of the railway operations.

"Concerns included the amount of established Buddleia which is particularly destructive to stonework, crumbling stonework and the poor state of the Twerton Station House, which is included on the B&NES Buildings at Risk List."

The group is now placing pressure on Network Rail to turn its attentions to repairs and, following a meeting, they have received assurances the condition of the listed buildings will be improved, with the buddleia and any stonework repairs a top priority.

But in the meantime, the group is determined not to let the original campaign for Brunel's railway to be retained on the UK list of nominated sites be forgotten and they also want it put forward as soon as possible for inscription on the UNESCO list of World Heritage Sites.

But Dr Christopher Young, head of World Heritage policy at English Heritage could not make any promises.

He said: "Whether or not Brunel's Great Western Railway stays on the UK's Tentative List depends ultimately on the Government review of World Heritage policy which is currently out to public consultation.

"This review will shape the character of any future Tentative List of potential nominations. The results of this are expected by early summer.

"Any future nomination would depend on support from the owners of the site."

A spokeswoman for Network Rail said: "We will continue the dialogues with English Heritage regarding their proposal. It is necessary that we review this and consider what this could mean to operating a railway fit for the 21st century and beyond. We need to strike a healthy balance."