I used to visit in the early-mid 1980s the large office building (non-aviation) Heathrow House on the A4 at Cranford. Inbound to 28R were pretty close and low on the A4 side of the building, but rooms further back gave a westward view of anyone on finals for 23L. Not a lot, but suddenly they would start passing by at close intervals, often for just a couple of hours, then stop again. The same company used to have another place by Wembley Stadium, and if 23 was in use they used to pass right over there as well.
I am convinced that one morning there at that time I saw a Northwest 747 passing by for 28R, which I worked out at length was a subcharter substitute for Malaysian coming in from Kuala Lumpur, but have never found any more to substantiate that. No documented lease, nor can I see any reason why Northwest would do it. Alternatives could be a Gatwick diversion ? White House press charter ? Any offers ?