I wouldn’t touch that car, not on those miles. You seem to be worrying about the monthly payments... where will you find the £4K to buy the car at the end of it, will you have the funds to pay for the car and save the 4K for it.
When you have to give the car back is it the same senario as a lease, where they charge you for over mileage or damage? Take that into account, you will have to get all that done or they will charge you a fortune for things like wheel refurbs and body damage,