I would suggest that you are being had over a barrel, and that a clutch should last more than 4000 miles - I.E. I suspect it was some sort of LR approved used vehicle, and thus tested before you bought it, by LR themselves, and assessed as "good"..... and then covered under some sort of extended warranty.
£1800 for a clutch is extortion in my book - there is a reason why they are all known as "main stealers"