Quote: "Shareholders may get to vote at the BAA AGM, but that doesn't mean they get to formulate government airport policy."
Government policy is for privately owned airports, and has been for ages, so they would be unlikely to nationalise LHR in order to close it. Any attempts to do so would probably be illegal and challenged in the courts. Years of litigation could follow.
Bearing in mind that the other alternative costs the government nothing, it is unlikely that the government would have the stomach (and the spare cash) for such a fight when there are other priorities, not least the economy.
Yet another U-turn is so much easier.