Pretty much any flying school will offer trial lessons, decide whether he would be more interested in seeing his house (in which case you'll want to pick the closest to him) or whether there is some other point of interest he wants to see.
If he really wants to take lessons then again, pick the school that he's most likely to fly from.
I think loop have a list of flying schools (not sure whether it's an independant list that anybody can go on or whether its advertisers only
www.loop.aero)
Given the issues with various schools, make sure it's more than £100 and pay by credit card....