Unless it can be proven that the clutch has been damaged by your friend's driving style, I believe the garage is 100% liable for this. And your friend is entitled to a repair or a full refund. The 2015 Consumer Rights Act covers the purchase of goods - including new and used cars - from dealers. It outlines the fact that the vehicle must be of satisfactory quality, fit for purpose and as described.

This Act gives your friend the statutory right to reject a new or used car (or anything else) within 30 days of purchase if their rights have been breached. This is called the short term 'right to reject'. For all of your consumer rights, see: www.honestjohn.co.uk/problems-with-a-new-or-used-c...s