Oh I feel for you...
Had mice (recurring) at my old flat. Yes, ground floor...there is a 2ft high gap under the floorboards, which is why it's so blardy hard to get rid of the little buggers.
Even fitted carpets don't help.
This house is Ok because, although we are mingers the floors downstairs are all concreted over, under the carpet - it is a 1920s house and there are boards upstairs which is fine, but downstairs not a whisker in 3 years!
Oh I tell a lie...we did have some mousey poos in the understairs cupboard once. I got everything out of it, crawled right to the end and cemented up a hole some B8stard mouse had dug through the concrete
I also filled any other possible areas of doubt. Nothing since.
I remember the familiar heart dropping feeling when you hear the scratching in the night.
The black and yellow plastic traps from Wilkos work really, really well...set up with peanut butter/chocolate spread (tis fiddly but Ok) and leave by a skirting board somewhere darkish.
I actually sat in wait - heard the rustling, heard the scratching, heard the deadly bang as it claimed mouse after mouse. A mother and 5 children within 5 days.