That's odd, last time I was at LHR, I saw 4 British registered a/c go past our KLM aircraft!
Blackball, and all others who think like him/her, I think you're just totally paranoid. Go visit the tower at any busy airport and you will find that all sorts of considerations affect departure sequences. And, since the large local carriers generally dominate the majority of movements, the ratio will be naturally higher in their favour.