Might be worth a read of this thread https://forums.overclockers.co.uk/showthread.php?t=18718503&highlight=nissan
I have called CAB, and they say i should get an independent assessment, but do no work to the car, then return the car for a full refund, doing so in writing, as I am in my 30 days from purchase.
They they have 14 days to give me a full refund.
When I make my next car purchase from a dealer it's going on a credit card Without fail, I guess there is a small percentage extra to pay but well worth it.
You only need to pay £100 on the credit card and the card company becomes joint liable for the entire purchase. A lot of dealers will allow you to do this without any penalty, but even if they did charge you 3% - £3 is worth it for the protection you'll get.
Surely they would be liable for the full £100, not the full value of the car?
The consumer credit act is a wonderful thing

Edit - and afaik you don't need to spend £100 on the credit card to get the protection. The goods just have to be valued over £100. You could stick a quid down on credit card for something worth £100 and get the full protection.