Sorry to hear of your problems and knowing how martinmac went through the hoops (to say the least) he is well placed to steer you in the right direction.
Looking back at your posts I see you said when you were buying the car that:
It’s 2007 model with a raised bonnet, 5.5k on the clock and asking price is £20k. BUT! It’s an ex-demo car of a Nissan dealership. I’m a bit worried of the amount of abuse it has taken for these 5,500 miles.
In which case I would suggest you go back the Plymouth dealership and given the weather has probably frustrated the roof operation, IMO I consider you should be able to argue you have been sold a car not fit for purpose, or at least put them on the spot that if it was their demo then the report back you have had suggests it was not properly looked after or checked prior to sale?
Do hope you get it sorted. When you say Wilson Automotive is that Wilsons of Epsom?