Ordered one this afternoon now having had a bit more of a think...I know what the car is like as two of my work colleagues have them (one a 280 and another a newer 290).
A 5 door Leon Cupra 300 for only £249 initial payment and £249/month, 8k per annum for 2 years is a good deal for the car you're getting I feel. No extra charge if you want a metallic paint option with this deal either (the only non-cost option colour is a rather dull blue, everything else costs £600 extra normally, but they aren't charging any extra for the optional colours if you sign up under this promotion, a nice touch).
I've some sums on what I can sell the MX5 for and decided to put a deposit down on the Seat. Less tax, better mpg, more space, practicality, refinement, speed and comfort than the MX5, without the worry of running a soon to be 10 year old car (the mx5 is starting to show its age a little in some areas now

). The Seat will be less 'fun' I'm sure but in every other way it suits me better.