I know you can haggle with VW over the interest rate, they were very keen (and did) beat my banks rate. One thing to look out for is that they will quote the interest rate as the 'straight rate' which may make it seem very low. For example 6% straight is roughly 12% APR. They ain't called stealers for nothing.
Sensible hat on for a moment, if you are thinking of getting a mortgage anytime soon, the bank will offer you less because you have this credit commitment. It would be better to get the mortgage first and then the GTI. I appreciate of course that its easy to take the sensible view when you aren't the one who's got his heart set on a new car. Been there and done that.
I would suggest as well that you try and sell your car private, even if you don't get any more money for it than you would as a trade-in, the garage will probably give you a better discount.
Its a long term commitment so def go for something that you want and will enjoy, even if it means you have to wait a bit longer before you take the plunge.
