I'm sure this has been talked about on another thread, but it's great fun.. I was the Air Controller for 09L at Heathrow when G-BJHS did a low run and go-around one day in September 1991. In the left turn out it crossed the M4 so low I knew we'd get some serious stick! Most stick came from the AFS - the fire station was north of 09L in those days and the Duty Officer rang up and harangued me for not warning them "as my boys would loved to have seen it"..
As for a Catalina with a magnetometer in 1977... sounds mega interesting and I wonder which one it was? I saw N610FF at Heathrow in 1965, picture here:
http://www.brendan-mccartney.fotopic.net/p22382311.html
The P51 replica was on a plinth on the roof gardens at Heathrow for many years but I've no idea of its fate when the roof gardens closed.