Bats are a protected species under the Conservation of Habitats and Species Regulations (2010) and cannot be disturbed. If owners want to carry out any building works which might disturb any resident bats they would need permission from Natural England.
Grey squirrels may also be found in roof spaces, particularly where surrounding trees give them a bridge into the roof and can cause all sorts of damage, nibbling on wiring and insulation etc. You may even encounter Dormice, which although cute, can be equally destructive! If you want further information on wildlife, their impact on residential property and licensing requirements a useful website is https://www.gov.uk/topic/environmental-management/wildlife-habitat-conservation