Andrew,
For a while, only Swanwick was used for Stage 1 - it's a cost-cutting thing primarily. Selection sessions were previously held all over the place but this often involved bookings for meeting rooms in hotels, etc and so this was stopped to save money.
Definitely no expenses for Stage 1, and I think it's the same for Stage 2 now, but get someone who's been through the process more recently than me to confirm that.