Blocking gaps in loft from the inside
Repellants may work here to get a mouse free zone.  If you have a friend with a cat ask them to give you a shoebox of used cat litter from the litter box and tell them to make sure to put as much of the litter the cat has pe ed on in the box.  That is very effective.  Other repellants are peppermint oil, cinnamon, cloves and apple cider vinegar.