I recently bought a 2012 Volvo XC60 from the local franchised dealer. It was their demo vehicle with 6500 miles. I explained I ideally wanted to buy new, but they had this on offer. They explained in writing and verbally it was 'as new' and exactly the same as a new car would be if ordered, ie a MY13 car.

On picking the car up, I noticed the V5c had the emissions as 149 whereas the spec said 139. The dealer said this was a mistake and they would correct it. However, on enquiring with Volvo UK it turned out they updated their engine after this car was made mid model year, and so it wasn't 'as new'- the new car has lower emissions and 7% improved mpg (according to spec).

The dealer admits the mistake but is very slow to come to a solution. It will a) cost me more to tax b) cost me more to run and c) may have an impact on the ongoing value.

What, fairly, should I expect them to do? I want to keep the car, and am aware under the SOGA I don't need to reject it to get a settlement. Any precedents?