A planning inspector was forced to abandon a demonstration of a canal bridge leading to the proposed site of 440 new homes on green fields near Bingley after it broke down – sparking fears it might have been tampered with.

Richard Clegg, who will decide whether developers will be allowed to build the controversial housing estate in Sty Lane, Micklethwaite, had to call off the planned opening of the swing bridge across the Leeds and Liverpool Canal when its safety gates would not close.

It would be replaced by a new bridge as the main access to the site if the planning appeal is allowed, in what campaigners have called a “crack-pot scheme”.

Terry Brown, who is campaigning against the proposed development as chairman of Greenhill Action Group (GAG), was on the canalside for yesterday’s failed demonstration, which was supposed to allow the inspector to see a narrow boat sail through the open swing bridge.

Mr Brown said: “For some reason the bridge is not closing. My concern is that it may be seen that GAG or somebody supporting GAG has tampered with it to prove the point about what happens when the bridge breaks down. I would not condone sabotage at all.”

Airedale Boat Club member Peter Saunders, who was operating the bridge, said: “It is not unusual for it to break down. The last time I came through, we were waiting for well over an hour.”

The bridge, in Micklethwaite Lane, will be crucial to the inspector’s decision following a public inquiry on whether to allow the appeal by developers Bellway and Redrow.

Campaigners say a new bridge will not be able to handle a huge increase in traffic if the homes are built.

There are also concerns that the emergency services would be delayed in reaching residents of the new homes if the bridge breaks down while it is open – blocking Micklethwaite Lane.

The developers say that Oakwood Drive will be used as an emergency exit from the site if the bridge breaks.

However, Mr Brown said: “We have heard at the inquiry that if the bridge is faulty, it will take British Waterways at least an hour to come to find out what is wrong with it. Meanwhile, nobody would be able to move off the site. Once British Waterways has decided, it will take the Council another hour to get somebody out to set up traffic lights at the end of Oakwood Drive. So for two hours the traffic would be building up. It is a farce.”

Diana North, who lives yards from the bridge in Airedale Mills, said she did not believe anyone had tampered with the bridge’s safety gates.

She said: “It breaks down sometimes and traffic cannot get through at all. That is the problem.”

A bridge engineer for the developers did not want to comment.

The public inquiry, which is being held at City Hall, Bradford, is expected to hear closing submissions from the developers and the Council on Tuesday.