‘URBAN explorers’ have taken shots of work carried out inside the old Queensbury Tunnel.

Campaigners are pressing for the 1.4-mile-long structure to be reopened to form the centrepiece of a cycle path network connecting Halifax to Bradford and Keighley.

And they have been fighting moves by Highways England to fill in the Victorian structure.

Norah McWilliam, of campaign group the Queensbury Tunnel Society, said: “We’re grateful for the insight provided by the urban explorers who have shown the extent of the works already completed to improve the tunnel’s condition.”

The society – which has been galvanising support for its plan to reopen the tunnel as the “jewel” in the multi-million pound Bradford-Halifax Greenway – says the photographs were taken during a two-week period when the tunnel was left unlocked and unattended for between half-an-hour and 90 minutes most evenings.

Highways England – whose Historic Railway Estates’ plans for infill have attracted more than 4,100 objections – has condemned the actions of the urban explorers.

“They compromised their own safety – and potentially compromised the safety of our contractors,” said a spokesman. “We discourage any further trespass into the tunnel.

“Despite the photographs depicting apparent safe conditions, the reactivation of the constructed culvert at Strines Beck over the weekend of September 28 and 29 has resulted in the tunnel being flooded to unprecedented levels. The southern section of the tunnel is once again inaccessible to our contractors.”

An online petition supporting the reuse of the tunnel has been signed by 12,000 people.

A decision is expected to be made in the coming months.

Queensbury Tunnel was built by the Great Northern Railway and was the longest on the company’s network at the time of its opening in 1878.

It closed to rail traffic in 1956 and has been named on the Victorian Society’s list of the top ten most endangered buildings in England and Wales.