I believe there is a procedure now called "The City Box". The "Box" is a chunk of airspace covering the area where the city departures perform the intial right hand turn eastwards while climbing to 3000'. Heathrow Directors cannot descend their inbounds below 5000' (thus leaving a 1000' buffer) if the aircraft will overfly this area i.e. those on a right base for 27L/R.
As far as i know the City box is only active when City is busy with departures and when it is active Heathrow directors bring up the box on the video map.