I think LHR just can't handle the demand anymore. Sometimes you're waiting in line 15-30 minutes to take off after being pushed out of the gate, and this is after 10 minutes or more after the time it was supposed to take off.
Also often you have to wait for a gate after landing - last time we had to get the stairs and buses after waiting for 20 minutes for a gate (international flight). The one advantage was we didn't have take the train after landing for immigration.