Car hire terms and conditions
Most car hire companies cover themselves with terms and conditions that say they can’t guarantee a particular make or model of car.
They often state that the cars shown are for guidance only and may be substituted for a similar or upgraded car at no extra cost.
Getting a specific car type
But if you've asked for a specific type of car - such as a large family one - and are presented with a small hatchback, the car hire company can't hide behind its terms and conditions.
In this instance the company wouldn't be able to say the car provided was a similar type.
Similarly, if you ask for a small three-door car and you get a seven-seat people carrier, the hire company shouldn't be able to claim this is an upgrade - unless you specifically asked for it.
Breach of contract
If your car hire company insists on giving you a car you didn't book, then the company is in breach of contract and you can make a claim.
You would need to show a loss as a result of this breach of contract though so you might not be able to claim if the company insists on giving you an upgrade, or a bigger car.
One option might be to hire the correct size vehicle from another supplier and claim back from the car hire company the sum you originally paid.
You might also be able to claim any extra cost over and above the amount you paid originally that you had to pay to get the same car elsewhere.