Yes, it is the Marine Timekeeper I. The movement from what I have read and have been told isn't in-house, but is a Perret. However, I understand that Perret manufactures these movements for the British Masters exclusively and they collaborate on all their movements, seeing that they're actually housed in the same building. Will probably need more confirmation on this though.
The accuracy is great though, as I gain about 5 seconds every 30 days or so, and the 7 day power reserve actually runs for the full 7 days.
Richard