I always presumed that the surname
Allison /
Alison just came from the fn
Alison (like other fns have been used for surnames, eg
James).
I was going to look up
Alison as a surname but I left my Oxford dictionary of surnames up in
Stirling and for some reason Oxford Reference Online only has it's firstname and placename dictionaries on the internet (very annoying as I haven't come across anything to beat it yet).