I know for a fact that in the mid 1990's one of the AirUK Fokker 100's (G-UKFF I think) had an MLS receiver installed for data gathering. There was no indication to the crew that it was there but every time the aircraft flew into Schiphol using rwy 06 the system gathered data from the experimental MLS system on that runway.
I would assume that BA were doing a similar thing with a variety of aircraft at Heathrow.
Last edited by Flap40; 17th Feb 2013 at 13:19.