I'm not sure about the bats as it was only a very small entrance at ground level, but wasn't really looking for evidence of them while there.
If it is used as a roost I'm sure it must be documented, they are highly protected by the Wildlife and Countryside Act. A few of the offences are below, even photographing them without a licence is an offence. Hopefully this is something the owner was aware of at the time.
- Intentionally or recklessly disturb a bat in its roost or deliberately disturb a group of bats.
- Damage or destroy a place used by bats for breeding or resting (roosts) (even if bats are not occupying the roost at the time)
- Intentionally or recklessly obstruct access to a bat roost.
Breaking the laws often results in fines (can be unlimited) and the chance of 6 months at His Majesties pleasure.