ok, so a call to Zurich Insurance on Monday.
Thanks for the replies.
Truth is I don't know how it happened. I was driving the car today to Dusseldorf, pulled back the sun-visor to reveal a small 1" crack at the top of the screen. Heart sank. Yesterday evening I went over a large pot-hole. I did check the wheels and there was no damage whatsoever - so I imagine this was when the screen was overstressed.
Either way, £700, £1000, that's excessive, but its not persuaded me to convert back to hardcore Speedster mode. Screen will stay.
Does the screen need to be heated? I had plain glass in my Caterham when I was racing it.
Thanks,