Hibernating bats already delaying demolition of the derelict Bradford & Bingley headquarters may prolong the process even more than first feared, it has emerged.

Because owners Sainsbury’s are aware of the protected mammals in the building, they must now wait until they wake up in Spring and then carry out full surveys of the Bingley office block’s nocturnal guests.

Shipley MP Philip Davies told last week how he was “bitterly disappointed” at any delay in knocking it down – which was scheduled for January.

And staff at his parliamentary office have now discovered further issues.

“After the hibernation period Sainsbury’s needs to commission a new survey and if that finds the bats are still there, they will need to obtain European Protected Species Mitigation Licence from English Nature,” a spokesman for Mr Davies’ office said.

And it could be that three additional surveys might need to be done with gaps of two weeks between each,” she said.

“This will bring it to the summer cycle when bats form maternity colonies which could mean that the demolition will not be possible or can be significantly delayed,” the spokesman added.

A Sainsbury’s spokesman confirmed that new surveys would have to take place and they would be working with Bradford Council’s ecology department to detail the number of inhabitants.

Bradford bat expert Ian Butterfield said hibernating bats had to be taken seriously as they are protected under the Wildlife and Countryside Act.

“This is not some weirdo EU legislation, it’s laws we have produced ourselves because bats are very endangered – we’re talking about extinction,” Mr Butterfield said.

“These in the Bradford & Bingley building are most certainly Common Pipistrelles, which are the size of the end of your thumb and could fit into a matchbox,” said Mr Butterfield, who leads bat walks around St Ives Estate and Denso Marston nature reserve.

“They like 1970s buildings which have plenty of crevices and holes to tuck away in,” said Mr Butterfield, a member of the West Yorkshire Bat Group.

And he agreed Sainsbury’s might only have a brief time to demolish the controversial building – due to the breeding schedule of bats.

“The female bats are already pregnant as they feed heavily in Autumn, then mate in October before hibernating.They emerge in April, then the females go into ‘maternity roost” in June, so there is only that window of opportunity,” Mr Butterfield explained.