Whether or not you have any rights in this situation depends on the terms and conditions of the seller, as the fact you have paid a deposit means they have entered into a contract with you.

However, the law suggests that if it is a genuine and honest mistake that you should have noticed then they are not obliged to sell you the item at the advertised price. It could be argued that an 84% discount on a car is unlikely to be genuine.

It seems unlikely that they would accept a claim from you that a contract has been made, so we would expect them to take legal action in order to avoid the loss of £10,000. It would be your choice on whether you chose to pursue this or not, but given you could easily lose the case, your deposit and end up with no car, it is arguably not worth the effort - assuming they are returning your deposit of course.