Originally Posted by
tobsw
Wow!
Well, it all depends who is operating your LHR-MAD-LHR sectors. According to the schedule I guess in your inbound it's BA operated, while outbound is IB operated. That means, you need to change terminals, from T4S to T4.
Your procedure will be as following: T4S BA arrival, clear immigration, take the automatic train to T4, security. You will be at the departure hall, where you can visit the IB Dali lounge. Your IB fight to LHR will depart from the lower H gates at the T4 terminal: there are a number of gates which are non-Shenghen, mainly for IB and IB Express services to EU-non-Shenguen destinations.
Anyway, you have enough time to do your itinerary.
You won't need to change terminals - IB LHR and other non-Schengen narrowbody flights have gates in T4S to 'board' from. You can clear Security in T4S, use the T4S lounge, then go to an S gate and be bussed to the aircraft parked at the low H gates. This saves you from entering and leaving the Schengen zone.