A colony of bats may have to be housed in any development at a former school site.

The creatures have been discovered at the old Whinburn School building in Keighley, which until recently was being used as a pupil referral unit.

Now the council - which is still to decide on the future of the site - is to liaise with English Nature about how best to deal with the bats.

The creatures and their roosts are protected under the Wildlife and Countryside Act 1981, and the Conservation Regulations 1994.

The strict laws make it a criminal offence for anyone to harm a bat, or damage its roost.

Bradford Council may be forced to accommodate the mammals within any redevelopment of the Whinburn plot, or build them an alternative home.

John Drewett - bat consultant with English Nature - has written to the council seeking information about its intentions at the site, and stressing the need for action.

And Councillor Barry Thorne, whose ward includes the land, is supporting demands for the local authority to ensure the creatures are protected.

English Nature was called in after a number of dead bats - believed to be pipistrelles - were found in the cellar of the school building.

Mr Drewett said: "Sometimes when bats get inside buildings - through holes as small as 15mm - they become trapped and die. They breed in buildings in the summer, but can't always get back out.

"When we visited the premises there were between 30 and 40 dead ones.

"Live bats will be in there but we have not yet established where the breeding roost is.

"Whatever Bradford Council plans to do with the site it will have to take the bats into consideration.

"If the building is converted the council will have to accommodate the bats within the conversion, or in the case of demolition an alternative breeding roost would have to be built.

"But in order to move the bats the council would have to apply for a special licence from Defra, and submit strong mitigation."

Councillor Thorne, who has raised the issue with Bradford Council, said: "The local authority has a legal responsibility to protect the bats, and I am keen to ensure that the protection is given."

A council spokesman said: "We are currently considering options for the future of the Whinburn building.

"In the meantime, our countryside and rights of way service will be working closely with English Nature to determine how best to ensure the well being of the bats and their roost."