It has a bit more substance than just a rumour. The Competition Commission report read as though it was saying BAA would be forced to get rid of one airport in the South-East of England and one in Scotland. I doubt Aberdeen or Southampton would be enough to satisfy them, so that means one of Glasgow or Edinburgh and one of the London area airports (and I think we can be pretty certain that they'll do all they can to hang on to Heathrow).
Which London area airport could be interesting. If Heathrow and Stansted get new runways, Gatwick wouldn't be that much lost capacity to BAA, but if Stansted were the one to be sold, Heathrow, Gatwick and Southampton would still dominate the area south and west of London.