Wow - I never thought this thread would generate so much interest, but thanks for the help. I thought I was 'caught' by a mobile camera van, so I would expect the officer (are they real ones in these vans?) to process the film that day. Here's hoping..
I agree that speed limits need reviewing in the UK. They date back to the 60s when there weren't the number of vehicles there are now. Open single carriageways are all 60mph for cars, unless signed otherwise. This is totally inadequate as often these roads are twisty country roads. Similarly, motorways have a 'design speed' of around 85mph, and yet they have legal limits of 70mph. All very strange. The problem with variable limits (ie different at night) becomes confusing for the driver unless they have variable signing, which becomes expensive to operate and maintain. No easy answer I guess.