John at About-Turn Locks. 07889157442. Highly recommend him.
Joanna S. replied:
Jim locksmiths on Surbiton Road.... Most excellent company. I bought new yale locks there and didn't know how to change them when I got home and at the time couldn't afford to have it done. They actually talked me through the process (getting the old lock off etc) on the phone whilst I followed their very patient instructions. 100% recommended,