Internal interview (although fairly generic process)
Usually 3 phases, face-2-face interview with 1 or 2 people, case study and presentation (sometimes incorporating a role play), and skills - depending on role
Your interview is really as good as the person selected for interview although the HR team prefer the manager to follow a competancy based approach: describe a time where you have... and you can expect about 5-8 of them. follow the STAR approach (it seems to be liked)
The people element varies greatly on area of the business joined although it is generally a relaxed culture. The social aspect of BAA is stunted by the fact that most people drive to work.
No cheap flights - so don't ask.