To add an alternative to the discussion, I have recently been hearing good things about Tech Auto carpets. See website here:
Classic Carpet Set Made to Order in Tufted Deep Pile for Rover P6 All
They also offer hessian-backed carpets (albeit with vinyl binding), but their colour range is bigger. There is a colour called 'New Ochre' which looks a reasonable representation of Mortlake Brown (more so than Coverdale's Kensington 'Wheat' to my eye). They are also substantially cheaper (£180-£280) compared to Coverdale (£430-£630).
I know the mantra is usually 'pay cheap, get cheap', but Coverdale's prices are are at least double what they were 8-10 years ago, which leaves me intrigued about Tech Autos.
A few people have told me the Coverdale carpets (even the top of the range Kensington) aren't a direct quality match for the original wool blend, so they may not necessarily represent the best value for money. Tech Autos are also handmade in the UK.
I'd be interested to hear from anyone with experience of Tech Autos quality and service.