In reply to Access BMC (England):
I checked this out today and it's actually Kestrels nesting in the route. So less criminal but please still avoid disturbing them! I've put a sign at the base for those same three routes - but dated to 30th June as they should have fledged by then.
Also, a couple of buttresses over, the Tawny Owls nesting in Oak Tree Walk will have fledged by now so I've taken the sign down there.