Not mentioned so far is that whenever operational constraints occur at LHR, whether it is due to an incident or the weather, it is, in my experience, the regional shuttle flights that BA will cancel first, leaving regional passengers connecting to long haul high and dry. This happened to me in poor weather one winter travelling from MAN to LHR and on to the mid-east.
So I avoid LHR and much prefer AMS, then FRA or the ME outfits for long haul from MAN. CDG I also find a 'difficult' airport to make a transfer at.
Of course expansion at LHR may mean that the cancelling of BA shuttle flights first goes away.