Hmmm... Extended warranty on a pair of speakers? Not much there to go wrong, and I'd check carefully the Ts&Cs to see whether there's a 'user abuse' get-out clause, as this is about the only way you're going to create any problems, unless there's a - rare - component failure.
And hang on just a cotton-picking moment!!!: assuming Richer Sounds are an authorised Tannoy dealer, the Tannoy website says "All passive components are guaranteed for a period of five years from
the date of purchase from an authorised Tannoy dealer subject to the
absence or evidence of misuse, overload, or accidental damage."
I'd ask for your £50 back.
[quote user="D.J.KRIME"]You have to like those guys at Richer
Sounds.[/quote]
Well, you have to admire their sales ability anyway, it seems...