I saw a bit of BigJetTV's YouTube stream today and, as well as a very clean looking Concorde parking up next to Envoy Avenue (near the Hilton Garden Inn), there was also a 777-200 parked with engine covers on in the maintenance area just to the west. He didn't get the registration but did spot an 'RR' sticker on the engine cowl. After a bit of sleuthing, it looks like it might have been G-YMMJ which has been parked at LHR since the 12th - any news on what's going on?

Interestingly (though not BA related), there was a KLM aircraft parked behind G-BOAB. Rumour on the stream was that it had engine issues and presumably couldn't make it back to AMS, so maybe it's waiting for some TLC from KLM engineers?