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Oh well, thanks for that everyone! I'll post my own answer, just in case anyone is going in the near future. The best thing about the gig was that the support act were not some rubbish "who the hell are they?" group- it was Aqualung, and they were really impressive, so I'd advise people to get there early so as not to miss them.
Dido herself was so much better than I'd anticipated. She had a great band with her, especially the lady on percussion, and she really does have a beautiful voice. Didn't hit one bum note the whole night. She really proved her musical ability too, playing the guitar and the piano during the gig. All in all, a very good gig, and a strange choice of song for the encore, but it really worked! Thumbs up.