how do i find a reputable locksmith?

[phoria]

google obviously but is there some kind of organisation they should preferably belong to?

I think it's called the Master Locksmiths Association. The window sticker is yellow and says MLA over crossed keys.

This lot
www.locksmiths.co.uk/

you can also search for "Chubb Super Centre Yourtownname"

Although the trade mark license has now expired, they tend to be professional businesses and well-established, and still comes up on some searches.

Thanks, PJ! This was just what I needed.