I think you could have some difficulties. If you suffer loss as a result of someone else's negligence, you have a duty to mitigate that loss - ie not take the most expensive option in making good your loss. Clearly rejecting the car and purchasing a similar one of a similar age and mileage will be more expensive in the long term (I suspect) than repairs. If the insurance assessor say that the car can be repaired, you will have difficulty persuading the ins co (and subsequently the court) that rejecting the car and claiming for the cost of a replacement was the least expensive option. Unfortunately, the law will only look at the effect on the car and not on how you feel about it. You could however obtain evidence of the comparison of values between a car of that age and value against a repaired car of that age and value and potentially claim for the difference, if any.