The answer will very much depend on the cause of the failure.

If it's a fault with the car then the dealer can be held liable for any problems that develop within the first six months of ownership. This is because the fault is deemed to be legally present of developing at the time of sale. That means the dealer will have to fix the car or give you your money back (minus a fee for the usage you've already had): www.honestjohn.co.uk/how-to-reject-a-car-your-cons.../

However, if the car ran out of oil or water then you will have no comeback against the dealer because this will be classed as (lack of) general maintenance.