Hi viscount, I think I was in the Potters Bar / New Barnet area of North London. The aeroplanes turned to look like they were on their final approach to Heathrow? My job as a train driver see aeroplanes every day especially when driving down toward Kings Cross. Initially they wer definitely side by side in formation, at first I thought it was a jet fighter shadowing a 747, but when I got a little closer it looked too big for a jet fighter and more the size of a commercial airline. On turning South the 747 did take the lead, but was closely followed by the other aircraft. If you take London as South from my location they flew in from the east to west, then turned South.