[Stooky Bill]

I know there are other ways to deliver alternate audios - for example, the DVB spec allows for different language soundtracks (which again, you'd access through menus in your STB), but I'm not aware of any UK broadcaster using these, and they probably don't have an easy method to transmit audio that way.

The BBC (and S4C?) have used a red button MHEG/OpenTV selector for alternate commentaries, which certainly used to boot you off into an SD red button stream. I don't think ITV have ever done this before though.

Maybe they do have something up their sleeves, but as Brekkie said above, anyone who's previously done live AD has had to use another channel for it. None of this should detract from the fact that they're making the effort in the first place however - I'm pleased to see more broadcasters recognising its importance.

BBC Alba have dual language sport, but I'm not sure how that actually appears at home, maybe a MHEG prompt? 

My understanding is that either the BBC2 coronation coverage has both AD and BSL so presumably the AD can just be mixed into the commentary without the need for a seperate audio track.

Although however it's done technically, the biggest problem with live AD is knowing where the gaps in the commentary will be. I suspect it'll just be someone doing a more descriptive commentary