thanks all and indeed i had heard long ago that it was something to do with Northolt , and I will ask in the ATC forum as you sat they are generally an open minded lot there.
I remember the fuss over noise a few years back having attended a public meeting on it where people made astonishing claims about being kept awake all night by the chanegs-of course there are no departures from LHR much after 10 30 or so.
On the other hand NATs?HAL didnt do themselves any favours insisting that all flights over Bagshot were well over 6000 feet overlooking the fact that a considerable number of BA pilots live in the area and were brought up short by a A320 captain who said that he routinely overflew his house at 6000 ft to avoid conflict with inbounds-and as to fate it seemed BA chose the evening for a specially heavy LHR-Capetown 747 to struggle 'low' and noisily over the meeting hall