Chris,
"Specialised car covers" (from whom I purchased my Ferrari cover, do 2 types for a Caterham:- 100% cotton (indoor dust covers only)at £145.00, in pale blue, dark blue Ferrari red, burgundy, BRG & silver grey. Apparently Caterham won't let them put the correct logo on the cover but you can have the Lotus logo.
Outside (4 ply) rainproof covers are £165.00 in grey only and with no logo.
I can vouch for these covers being excellent quality as I already use them myself. Any other leads ?
Jules