In my previous job I dealt with notices of intended prosecution for speeding fines (and dangerous driving, running red lights etc. - I worked for a car hire company) so I can pretty much quickly say some stuff here that I witnessed on the hundreds of police notices I've seen.
*Will I get a ticket?*
i) If you were caught going 5mph+ over the speed limit by a camera, yes you probably will. I only ever once saw anything below over 5 (it was 4) and that was dealt with by an officer not a camera.
ii) Most notices of IP are sent out within a week, if you haven't had one after two weeks then consider yourself blessed.
*What options are there*
i) If your area offers one, you can pay to do a speed awareness course providing you didn't exceed the speed limit too excessively (I'm sure the maximum is worked out by taking the speed limit, adding 10 percent of that and then plus 9? So in a 30mph speed limit you could do a maximum of 42mph to be eligible for course).
ii) Pay an upfront cost of a fixed term penalty and accept the points on your license.
iii) Challenge it in court.
iv) Nominate the driver/the owner of the vehicle if it was not you.
*But I wasn't going that speed, my car showed X speed*
i) The general response to this is that all stationary speed cameras (and hand held ones) are subject to home office approval and thus it does not matter if you thought you were going a different speed in your car, they go by the government approved police device.
*How long do I have to reply*
i) One month to reply to the notice of intended prosecution. If you get a form please fill it in correctly, because if you don't they send it back to you without extending time scale.
*But I was only going 22 (ex) in a 20, surely that's not illegal?*
Whilst it seems arbitrary to charge someone for it, it is still technically illegal and they have every right to prosecute.
*Meh it was only 5mph over, I don't think anyone will be that fussed*
In my previous job, a heck of a lot of notices were from speed cameras that had caught people going dead on 5 mph over the speed limit. Please don't be a fool and think you can get away with _5mph in a _0mph zone, it's not worth it.