There was some specific advice given by the CAA on the use of transponders a while back. it was given in the December 2002 of GASIL
GASIL
Check the top of Page 11. The old advice was to use transponders all the time squwaking both Mode A and Mode C
except in the visual circuit. the latest advice is to keep a serviceable transponder on squawking 7000 Mode C unless:
*ATSU has allocated a different code
*A special purpose code is more appropriate
*Local procedures require the transpoder to be switched to 'standby'
So now the advice is keep it on ALT unless instructed otherwise.
It also says the UK AIP is going to be amended to reflect this recent change.