Ken Duglan could most likely help. He runs the Atkin Grant and Lang gunstore which is located on the Broomhills clay shooting club ground located just off the highway number A1 which is north of London about 40 miles. Its on the route down from the north and is open during the week. I collected 2 hammerguns from him there last year and it looked to be quite a good range.

http://www.atkingrantandlang.co.uk/

Martin