Presumably a diesel? Most manufacturers attribute failure of DMFs to clutch failure caused by driving style, even though the real villain of the piece is usually a failed/leaking clutch slave cylinder that is never returned with the other failed parts.

I've been on TV about this in 'Don't Get Done, Get Dom'. Without all of the parts, unfortunately you have no proof. But if the failure occurred within six months of purchasing the car, consumer rights are on your side and you can hold the dealer liable: www.honestjohn.co.uk/faq/consumer-rights/