Join Date: Oct 2006
Location: London, UK
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Posts: 16,873
Not all (but most) T5 longhauls operate from T5B.
If you are arriving from another terminal, you will arrive at T5A (the main T5 building). Screens inside T5A will typically show 'Go to B Gates' when they know if the flight is departing from T5B. In T5A there are the North (Club) and South (Concorde Room, First and Club) Galleries lounge complexes.
Once the screens show 'Go to B Gates', take the transit to T5B, where there is another Galleries Club. If you are oneworld Emerald or travelling in First, however, you should stay in the South Galleries lounges in T5A until around 15 minutes before your gate closes, as T5A is where the Concorde Room and Galleries First lounges are.
IIRC, all buses operate from T5A (typically Gates 4b and 10).