Originally Posted by
eyeinthesky
Unless this is a local agreement I know nothing about, I would STRONGLY discourage you from:
"Besides if you intend talking to Farnborough you can squawk 0447, this tells Farnborough you will be contacting them ASAP."
You should not select any discrete SSR code without instruction from the ATC unit responsible for it. You risk confusing them and misident against other traffic.
Has been the case for quite a while that
0447 used for EGLK departures, 0457 for EGTF departures. (i.e. non-circuit traffic, expecting to call Farnborough LARS for FIS/RIS/RAS rather than Heathrow/SVFR or NORDO 
).
7 years maybe?