Locking the J toilet door

[Daver6]

Would that announcement been made to allow J passengers to use them 1st to change into their PJ (basically to minimise the line)

I don't think that was the reason. Flight leave LHR around midday, so the cabin doesn't go dark for a good 5 hours or so post departure. Where that idea would be more useful would actually be prior to London.

I think it was either to not get in the way of the meal service (I really don't see that being an issue given carts aren't used and Y+ pax only need to pass two rows of J to access the loos). Suspect maybe just to give a more premium J experience.

I was in row 1 for this flight so I can't comment if there was much difference. On the way to LHR I was bulkhead in the rear J cabin. There was no announcement made and in all honesty, I can't say the Y+ pax using the J loo made much difference to my experience.