East St Cycles have repaired my wheel for free :-) nothing, nada, zilch, zip.
Apparently they've spoken to Trek who believe it was a structural failure of the wheel that should not have happened and have covered it under warranty. The wheel has been completely rebuilt with brand new, stronger spokes although they're now silver and not black but I'd rather have a wheel that lasts longer. I may see if they can do the same for the front wheel but it's not too important.
As an aside, perhaps I should offer them some web design/hosting services. They've had the same static page for nearly a year now.