This is far from a done deal.
Have to say, I disagree entirely.
Regardless of whatever concerns nationalist parties may have (legitimiate or otherwise) the combination of 3 major UK broadcasters working together with the 3 main political parties represents a pretty unassailable proposition.
Whether the nationalist issue gets addressed or ignored, there is now such a level of expectation amongst the public for these debates to take place, that there is absolutely no room for broadcasters or party leaders to renege or prevaricate.
I'd put money on these debates happening.
I'd be more careful with your money.
It was a "done deal" in 1992 and 1997 as well.
Brown has said yes because otherwise he would be the toast of the Tory conference this week for "hiding from debate". Even if legal challenges fail, Brown (who clearly will come off worst in a TV debate) will have a million other reasons to not proceed based on the rules of engagement.
There is so much minutiae to be agreed and therefore disagreed on: how much time to answer each question uninterrupted? are there questions from an audience? is there advance warning of questions? is there even an audience? how long for cross-exchange? does Clegg get less time to answer than the other two? who gets to stand where on the podium- is it brown-cameron-clegg? but then why does cameron get's to stand in the centre- surely unfair prominence?
You can see the nightmare the broadcasters are going to have, especially if, as I suspect, Labour only want to convey the impression that Brown wants to take part. No labour strategist would choose a TV debate for Brown- he has virtually nothing to gain (can't hide from governing record) and lots to lose (he looks scary on TV!). The former reason is why Major and Blair both blocked these debates.
Now Sky have said they will proceed even if Brown pulls out, leaving him an empty chair on stage. Three points:
a) this assumes that Cameron will proceed against just Clegg (risky for him- expected to "win" therefore little benefit for him, but potential to slip up)
b) also assumes that Cameron and Clegg can agree terms
c) Brown knows that a Clegg-Cameron debate is meaningless, and that ITN and the BBC would never proceed to empty chair him.
Sky's rather odd political campaign for a leaders' debate (actually a publicity campaign for the channel) is meaningless - very few will watch a Sky debate of two opposition leaders in the context of no terrestrial follow-up. If Sky News had any significant influence on voting patterns, Hague's self-destruction in front of Adam Boulton in the 2002 campaign would surely have resulted in him actually losing seats compared to Major's poor baseline.