I had looked up the terminal map, lounge locations and LHR Ay departures. LHR departures pon AY go from gate 31 which is in the Non-schengen area past passport control. As Is the Long-Haul lounge. And that is what I intend to use. Good to hear from the previous posts that is consistent with others' experience.

We don't really intend to spend too long in there anyway (and quality of alcohol won't be a priority at 7.30am on Sunday with a toddler!).