LHR Transfer T2 to T5 (both domestic flights)
I was making a transfer from a Flybe domestic flight (T2 arrival) to a BA one (T5 departure).
The bus from the Flybe aircraft deposited us in a domestic area of T2. I had hand baggage only, so I followed the 'Flight Connections' signs the short distance to a waiting area for a bus to T5. I caught the bus, which then picked up more passengers from two stops nearby (T2 international?) before making the journey over to T5. On arrival, I followed the 'Flight Connections' signs for domestic flights and found myself at a UK Border point with passport checks. I had my passport with me (I'd used it as I/D on Flybe), so I just used it to pass through the gates as directed by the attendant, without really giving it much thought.
A couple of questions occurred to me later:
1) Had I gone wrong somewhere? It doesn't seem quite right that I had become an 'international' passenger?
2) What would have happened if I'd not had my passport with me?