Timing of showing adverts with celebls

[mardyfish]

Maybe I am imagining this, but I seem to remember that a couple of years ago there was some fuss because during Big Brother an advert was shown in which Davina McCall and Dermot O'Leary did the voice over and apparently adverts were not meant to include people who are also in the show on round the advert.

Was that the case (not the specifics of that example, but the general rule) and if so has it changed as for example during the X Factor adverts with Cheryl Cole and Danni Minogue are regularly shown...?

Any clarification or explanation would be very much appreciated - thanks in advance

[Blades_fan]

I've also noticed it,Ant and Dec advertising Nintendo during I'm a Celeb.
Seem to remember Channel 4 being fined a few years ago for showing an advert featuring Carol Vauderman advertising some sort of yoghurt in a commercial break in the middle of Countdown.
I think it's the Advertising Standards Agency that oversee it,but it must be ok as it's pretty rife.

[Blades_fan]

I think voiceovers have always been ok,but not the actual person appearing on screen.