Walsh's article quoted by Dave Reid above is quite interesting. He says the case for doing Heathrow is stronger than Gatwick but the politics are more difficult and he doesn't think Britain is strong on political will.
Would he be saying that if BA really really wanted R3? Maybe not, but I don't think he has yet said in terms 'Don't do Runway 3'.
Perhaps that's another Mandy Rice Davies quote -- he wouldn't say that, would he!