Originally Posted by
ratypus
No, I doubt it...the boarding pass which does entitle you to lounge access will (by the time you return to LHR) be in respect of a flight that already departed LHR, and your onward boarding pass will not entitle you to lounge access.
I think this is the relevant point. You can't use an outbound bp for a flight which has already departed to access the lounge.
The point about connections going from F/J to Y is that you are using an inbound bp rather than an outbound to gain access.