I had a bit of a brain fart with this one, and it took a friend to point it out, sadly I didn't take many photos, so you'll have to be patient with my explanation.
Let me try and explain......
After fitting the rear hub it was time to fit the rear brake disc assembly and clamp it in place with the hub nut and driveshaft washer. Pretty straightforward, I removed the calliper beforehand and fitted the disc assembly over the driveshaft splines until the disc was fully home and then secured it with the hub nut and washer. You can't achieve the required torque setting on the hub nut until the car's handbrake is installed, so pretty tight will have to do at this point. The hub nut is a 42mm so you will need the corresponding 42mm socket. I had to source one for the task as my largest socket was 32mm. I also needed an adapter for the socket as the size ends up at 3/4" drive.
Afterwards, I went onto reinstall the rear callipers. I took this opportunity to install brake pads into the callipers too. This took a little head scratching to work out how the pads sit in the calliper, it became apparent it was easier to split the calliper and hanger to fit the pads. Caterham shipped the calliper whole, so it kind of gave the impression it was to be fitted whole, but in fact the assembly instructions show the calliper and hanger split, so I guess you are supposed to split the assembly. It certainly made fitting the pads a doddle.
My problem was fitting either over the disc and then securing everything in place. No matter what I did there wasn't clearance. The disc was sat outboard too far, even though the disc was fully home on the hub. Nothing I could do seemed to solve the issue.
Eventually my mate Mark popped round to take a look, he is very experienced and usually solves these sorts of conundrums. Mark immediately suggested the calliper required spacing out, but I was convinced that would not be the case, of course, he was correct and I was wrong. I'd missed two tubular spaces required between the calliper and the ear, using these gave sufficient outward spacing to easily sit over the disc. Even now as I look at Caterham's diagram they aren't easy to spot, but they are shown, doh!!
Once the spacers were inserted as required everything assembly easily as per the diagram. Problem solved.
Of course don't forget to use some copper slip on the rear of the brake pads, and remember the driveshaft nut requires fully torquing at a later point.
Thanks for reading and I hope this brief post helps you avoid the same mistake.