I've been to free gigs at HMV Oxford Street, if you really want a good chance to see him (cause they only give out like 75 wristbands), go when they open at 9AM on the day of the gig, you can get the wristbands from the main registers (tills?, I can never remember the term) and buy the cd you are to have autographed in the morning, cause once I didn't do that and it was HELL getting the cd as there was a MASSIVE queue to see the artist that I was seeing.
Good luck and post all about it!
Manny
xoxoxo