London Olympics organizers attempting to get opening or closing ceremony performance commitments from a number of Rockers got shot down by several, most notably the Rolling Stones.  They did manage to get Paul McCartney for the opener and to slot Pete Townshend and Roger Daltrey in Sunday's (8/12) closing ceremony (story).  Rumors about a possible appearance by members of Pink Floyd circulated and were dismissed, but that still appears possible (story).  Mick Jagger attended some track & field events with his son but was mum on doing anything beyond being a spectator.
So, the question: with this being the last and largest world-wide event being staged on home turf in the lifetimes of so many pivotal (and in many cases egotistical) members of British Rock, have more of them committed to a surprise performance?  Pulling it together and pulling it off without word getting out would be monumentally difficult - but it is exactly the kind of thing the Brits would love to spring on an audience.  And imagine the possible array of participants.  Probably not going to happen... but if it did, what a moment it would produce!