Originally Posted by
CUPPSIT
Having to escort passengers who have missed their flight back out of the departure lounge costs time & money (to some combination of the airport/airline/handler) so everyone wants to reduce it as much as possible
Loads of airports have a really cunning solution to this "problem". You are allowed to exit the airport yourself, as if you were an arriving passenger (i.e. through any applicable border controls). Doesn't cost time and money if you lay the bl**dy terminal out properly in the first place!
I suppose T5's designers were
so desperate to allow UK Domestic pax full access to all the shops that having a segregated area for Domestic flights was ruled out early on...