I'm also South UK - Oxfordshire.After 14,000 miles I changed from PZero to PS4's - they were down to the 2.5-3mm level. I then sold it - Oh well. I did think wow the PS4's are way better - (of course they were newer and the placebo/internet effect!).
My new car has P4Z's. Super happy, I feel as confident in the twisties as I did with the PS4's. And it is winter too!
This is my first sports car, on other vehicles I've always pushed tyres close to the legal limit (when I was a teenager I went past the legal limit... but the tyres were the least of the issues with my old Rover Maestro!). Does that extra 1mm really make that much of a difference? This is a genuine question.