I think it's very difficult to give a figure on this Bob, depends very much on whether the car is used for stop-start inner city driving, or spends all it's time on the bypass in top gear.
My previous Astra van (often used for towing 1000-1500kg, but always long trips) was still on it's original clutch when I sold it around 185k, yet I know of a dear old chap that managed to burn through a new Ford Ka clutch in just 7k...
Unfortunately, he was becoming hard of hearing and the Ka didn't have a rev counter, so slipping the clutch became a regular occurrence ! Ford agreed to replace it under warranty but specified they'd only do it once
I put a new clutch in my Discovery (again, always towing, as you know
) around 160k due to a squealing noise. However, that turned out to be a loose mounting bracket within the bellhousing, whilst the original friction plate looked like new with the manufacturers grooves still clearly showing. But having removed the gearbox, the new clutch and DMF was fitted anyway.