Pipistrelle bats are the most common in Britain

Yorkshire Water had planned to demolish the former dam-keeper's cottage they were living in during the �7m project at Linley Wood Reservoir in North Yorkshire.

The plans were altered after engineers found the pipistrelle and brown long-eared bats in the building's roof.

Now the company has completed work to raise the level of three dams at the site in the Washburn Valley, the mammals will be left in peace.

Bats are a protected species in Britain, though the pipistrelle and brown long-eared variety are not under threat.

Yorkshire Water applied for a bat licence in summer 2002 to allow them to temporarily disturb the bats as they carried out the work.

The ground floor of the cottage was filled in through a small window during the project, keeping the bats' base in the roof intact above the water level.

The pipistrelle is Britain's smallest - and most common - bat and can catch up to 300 insects a night.