It was a three stage process with the first being a 30 minute informal chat with their Internal Resourcer. The second stage was a technical interview and discussion on how you work as an engineer. This was with the department head and their chief engineer. The final portion consisted of an interview with the Technical Director going over some typical interview questions but also discussing engineering as a broader topic.
All in all it was nice to have technical conversations with engineers who know their stuff and are passionate about the sector. The Internal Resourcer is very helpful throughout and really puts you at ease. I regrettably turned down the offer but only on the basis of other opportunities fitting my arrangements better.