When some of the channels they broadcast start delivering content in HD, I imagine. The BBC is doing HD trials at the moment, but don't expect anything for some years yet. Unlike in the US, the T industry here declined the option of adoptiong HD at the same time as digital, saying it would cost too much and cause too much upheaval.
Your lovely new TV set will only reach its full potential if you buy one of the next generation DVD players, when they come out, and a fistful of HD-DVDs to play on it.
Personally I wouldn't have bothered buying a HD telly at all ...