Thanks again chaps, you are right and I've basically done as much tonight.
There are 3 BMW dealers making me offers (although they all come out about the same) all of whom I've had a conversation with tonight. When I spoke to VW earlier they were frankly rude, they were very formal and dismissive of my questions.
I'll pick a BMW deal tomorrow or Saturday if its one from the chap who is away tomorrow and as soon as I do I'll ask VW for my deposit back, which I confirmed earlier they would do. VW are being too arrogant. They know they have the demand and they can do what they like. If I cancel so what? They know they can re-list my car without any discount and still sell it. In a way its a monopoly they have.
Told my dad about my decision and he thinks VW Germany kind of 'intentionally' fail to give VWUK proper information and will leave them to the bottom of the heap in terms of support. From when he worked in the industry he says the German manufacturers have a massive superiority complex and basically think of themselves as the kings of the car and the UK as the lowest of the low. They're also making vast amounts of money from the UK market. The above applies to BMW as well I guess but perhaps a little less on the providing information front. Or at least I hope so!

Its a real shame about the GTI but at least I'm so annoyed now that I don't feel regret. I think I will be writing to Mr Thomas to explain what I think of VW though. Purely for his benefit if he wants to try to improve customer experience.
I'll have to change my signature soon I guess!
I also want to say good luck to all those sticking with the GTI or GTD. I still believe both cars are fantastic and my decision to call it a day is not a reflection on the GTI and doesn't mean I think it would be the right decision for any of the rest of you. I guess I'm saying I hope no one takes it personally that by posting this I am criticising their decision to wait it out. And I'm sure you'll all really enjoy your cars when they arrive.