I've just bought a ticket from MegaBus but accidentally put it through for the wrong dates.
It cost me a total of 50p (!) which was the reservation fee so it's not a huge loss.
Of course, if somebody else wants it, they can have it for cost!
Depart Coventry, Cannon Park at February 7, 2011 6:05 PM
Arrive London, Victoria Coach Station at February 7, 2011 8:30 PM
BT or PPG, whichever. I will email the ticket information over to whoever buys it.