I've just searched 'Rat' and it seems lots of us have had little ratfink visitors recently.
I've just found what I think is a rat hole at the side of our brick-built extension, underneath. Hole is about 15cm wide and something has clearly dug it.
Could've been there for ages. Extension built 5 yrs ago. I've only cleared it that area as we're having a new boiler fitted and that's where the vent is. I've since cleared all rubbish / leaves away.
I had rats as pets for years so I'm not particularly squeamish about them. We're in a terrace & I know they're everywhere. Just don't particularly want them in the walls / ceiling!! No noises, scratching or any other signs.
Do I need to do anything else?? I googled it and apparently rat holes by buildings are generally them getting out not in but no idea if this is true!!
Shall I plug up the hole?? Don't want to trap any rats lurking down there in and force them to chew further under the extension 
Not getting traps or poison as we have a dog & lots of cats in the area. Ironically, DDog is a ratter-terrier breed. But lazy and mostly useless so would probably just make friends with it.
Shall I just leave it be?