The prevailing belief is that LHR is truely full and ALL slots are used.
This is infact not the case as there are still slack periods in the day admittedly off peak when the arrival runway CAN handle the additional summer schedules !
Its these times when the airlines with just a few flights a week typically North African can be accomodated with ease !
So there is room for Eithad , Gulf Air and China Eastern without cutting back elsewher still!