Cheers Bob, 322 worked nicely, well almost. Pressing * and TV flicks from the cable input on AV1 to the aerial input. Unfortunately it doesn't go back again. I'd rather have it that *-TV cycled through the various inputs on my TV, as a button on my TV remote does. But I'm not really sure if the fault here is NTL's or Sony's (not having a manual, I don't know what the *-TV combination is supposed to do!), so I guess I shouldn't really complain.
Also, further to my original response, while the grey remote uses the IrDA-ish protocol to talk to the STB, it does of course use RC4/RC5 to talk to your TV
EDIT: One last thing. Is there is key combination on the remote that functions as "hold" on Teletext pages? Cheers