Now this is a can of worms. They can’t, but G-GATJ is still “British Airways”. There are 2 left at Gatwick that haven’t been transferred just yet, (I’m not sure the other reg off the top of my head). So there is a tiny sub portion of crew operating those flights on these 2 airframes, these crew can legally operate at LHR but not EF frames. The pilots are ex Gatwick base but not officially Euroflyer and some will be “swapping” to Euroflyer, others will return to LHR in a month or two. For the other planes at Gatwick they couldn’t do this.

I would hypothesise perhaps the LGW based cabin crew have virtually all done the swap to EF and as such some LHR are standing in until these final 2 frames swap AOC.