Thanks for that. I found an option on my TV called "Power On Preference" or something along those lines with an option of "TV" or "AV". I've seen it before but it's never seemed to actually do anything. On closer inspection though it does actually bring the TV on in "AV" mode ready to accept input from the coloured buttons. I've always dismissed it before because even though it's in "AV" mode the TV still displays the input from the aerial until you actually press a coloured button.

Anyways, I've just changed the input select on my AV device to press the coloured button twice for each input (once to bring up the menu and again to select the input) and am completely ignoring TV/AV because, in theory, it should always be in "AV" mode now. We'll see how it goes...

Thanks for the link anyway. If my method fails I'll be doing that.