I just connected through LHR. At the connections desk (when you arrive at T3 via the FCC) There was a cardboard sign on the counter behind the agents advertising "Upgrades to Executive First...etc. Ask us how." It clearly listed two prices (I don't recall the exact amounts but it was something like 389P to points East and 489 to points West.
It was not obvious over on the back counter, I wonder if they only pull it out to a prominent place when necessary.