Well done, Paul. I listened intentively too when I heard your dulcit tones.
I would give you a 7 to 8 out of 10. I liked the #1 comment about damaging the Police's reputation and standing in the eyes of the many (were you thinking of me???).
He was hard on you but I like the way you used the phrase 'suspended disbelief'.
My only real, major criticism is that you din't actually get to say the web-address. Would have been a 10/10 if you'd said something along the lines of "All our (unbiased) research can be found on the SafeSpeed website:
www.safespeed.org.uk - we also have a large public forum too where you can see just how much damage this is doing to the police................
Only one other point I can think of: When the interviewer started rambling on about how unconditionally obeying the speed limit would be wonderful, you could have burst his balloon by saying something like "I wish to make it clear that the SafeSpeed campagn is NOT advocating, in any way, shape or form, people be allowed to drive at 200mph through the streets of Bristol (or wherever).
But well done - it was a good performance overall, and you certainly did better than I could have done.