It may be a baby bat. When we had one in our house years ago,we were told that the young ones can get lost before they develop all their sensory talents.
But,this seems rather early for baby anything.
I've contacted the RSPB and they said it's pretty rare for them to be out and about at this time of year. Its chance of survival are pretty slim as I noticed this morning, as it nearly got snaffled by a magpie.