Just passed through the ATC Forum, saw the MR link and no-one, other than Heathrow Director seems to know the story. As MR made me 'famous' I will furnish a few facts.
Briefly, he was a back-up shuttle using callsign, mid eighties, when Tony and I, on Heathrow Approach, forgot him off Bovingdon for 09L. When we finally recovered him, we agreed, from that day, to adopt him on A Watch. G-MR, whether inbound or outbound never held. Pilots never understood it, but quite liked piloting MR as they got home earlier. This is the short story. The full story is too long.
On my retirement, in 2002, I was presented with the full registration, taken from the actual aircraft, along with a control column. The registration hangs on my garage to this day and, in fact, I am taking it to Brooklands on 20 August as I am relating the story at a 'do' commemorating the first flight 50 years ago of G-ASHG(the prototype) - if I can get it in the car!
For Info
ATCO Two posted the story on P-PRUNE, 13 September 2000.