As I understand it, the area between T1 multi-storey and The Station will become a new multi-storey car park with the existing T1 and the existing T1 multi-storey becoming an enlarged T1 linked with T3.
I haven't seen plan myself but I would guess that the new car park will be built then the old one demolished. That area would become a new check-in and maybe security allowing for a much larger lounge area in the space currently occupied by the current lounge, security and check-in.
Could be wrong though!
Gavin.