Cuillin.. No one airline is a "culprit". Flying into Heathrow early in the morning is a very busy task and CDAs are almost impossible. Both runways are usually in use for landing and there is a major problem separating traffic which may be crossing over other traffic for the different runways. For this reason some aircraft may have to expedite their descent whilst others may be held high while someone goes underneath. There are no set procedures for all this - it's all straight out of the radar controllers heads.