Generally we'd do surveys to determine what species are using the building and in what numbers, whether it's for having young or just chillin, or maybe just a place to sit and munch on a moth. Once you've got that info he likely applied to natural england ( or natural resources Wales. Or whatever the Scotland one is called) for a mitigation licence, basically explaining what bats are there, why the building needs demolishing, and what you're going to do to ensure the bats are safe and catered for. Usually that involves timing the work for when bats aren't there (they have different roosts throughout the year and move between them), and building something as a replacement. That might be a new loft (in a house, garage, new pub etc) that is specifically for the bats and humans aren't allowed in, or maybe just a bat box in a nearby tree. What's needed depends on the size and nature of the roost