I am based in West Kent, but theres quiet a few gunshops based around Tunbridge Wells, one of which specialises in antique stuff and is well worth a visit for the dribble factor
These two are in TWells, might be worth a phone call
http://www.pantilesguns.co.uk/
http://www.gun.co.uk/
The Gunsmith I used to help out delivered to GT Guns in Cousldon, they do list a BP section
http://www.budgetwebsiteservices.co.uk/gt/index.shtml
Theres also two shops in East Grinstead, one in West Malling and another in Biggin Hill
http://www.egguns.demon.co.uk/
http://www.faanderson.co.uk
http://www.the-internet-pages.co.uk/.../guns+fishing/
http://www.bigginhill.co.uk/saddlery.htm
Difficult to say who is worth a visit, but they should answer to email or phone calls. The Pantiles shop is well worth a visit, just to see some real works of art.