I spoke with Simon from Caterham Midlands yesterday, and he gave me an update on what they found.
Having received the car back at their dealership, Simon looked under the car and was immediately surprised with the amount of oil on the floors, he then put the car on the ramp to take a closer look. After a thorough inspection it transpired the rear diff cage (lower mount) had broken - (which I remember reading on Blatchat some time ago) was a potential recall issue, so I'm not sure if I had received one of the remaining ones that hadn't been recalled or had the necessary fix.
Anyway... The broken diff cage has pushed the propshaft into the rear of the gearbox, which has then worn the prop and the rear of the box, meaning both of those parts will need replacing too.
The long and short of it is, the engine and gearbox will come out, the gearbox tail will be replaced, the prop shaft will be replaced and so will the diff cage... Thankfully Caterham are covering all of this as a warranty repair, so the only bill (should) be for the first annual service.
I'm glad I'm not in a rush to have this fixed as it's a big job... but hope to have the car back around the third or fourth week of July.