UPDATE
Body shop was about to begin the job but found the roof welding coming adrift and it was not laser welded, meaning the roof had been replaced at some time (badly). Body shop approached VW for more money to replace the roof but the claim was rejected outright. The quote for roof replacement is £2500. I just don’t want the car anymore so the fight begins. I have already been told by the dealer that a full refund is not an option. OUTRAGEOUS! this is fraud.
Surely you can reject the car under the sale of goods act? You have only just found out that this car has this fault and I for one wouldn't be happy to have a car where the roof welds were faulty and replaced. The roof is an intrinsic part of the safety cell and the rigidity of the car.
This is clearly a cover-up of a dodgily built motor and one that is IMO unsafe to market too.

Contact WHATCAR. I'm sure a disgraceful situation like this is right up their alley. It's time to shout it from the rooftops and the louder you shout, the more they will squirm. If you sit back and wait now, you are only doing your case more harm than good.
I really do hope you get a good result from this, as it is p1ss poor situations like this that REALLY get me going
