I need to get back to them to ask why they lied about not covering cars over 5 years old and why they are operating double standards. I had hoped that I would hear of lots of people having got it done completely free, but I've only found one.
I'm not letting this one drop, so they have one chance to make things right. If not, I will get the work done (£217 quoted), and pursue VW via the small claims court whilst involving the likes of pistonheads and honest john et al throughout the process. Getting VW in the media spotlight might force them into being fairer about how they decide whether or not to repair a car.
One thing to be careful about - if you leave it too long pursuing VW, that £217 repair will become more like £1,000 for a new tailgate as the rust keeps spreading