David,
Thanks, my wife hates them, I quite like them.
The idea was to make the Plus 8 a real "all year round car", I love driving her, she is waterproof and warm and with SSL's suspension upgrade and 40 section tyres, comfortable and quiet!
I used 40 profile tyres on the 19" wheels, this gives the same overall size as 19" and 35 profile, I'm told.
I don't think there would be enough clearance under the rear wheel arches with 40s on 19".
Why change the wheels? 19" M&S tyres are not easy to find, and more importantly I don't believe in changing tyres, rather wheels and tyres.
Ihe 18s have far more options and I was able to buy them at a good price!