If caught by a police officer, you may have to wait for the paperwork to arrive in the post. It usually takes around fourteen days (two weeks) for the Notice of Intended Prosecution to arrive. Once you receive your Notice, you have 28 days to respond. In some circumstances, you may be able to pay a lower fine if you respond quicker to the Notice.
If caught by a speed camera, the process is slightly longer. Within fourteen days, you will be sent a Notice of Intended Prosecution, which is a letter sent to the registered keeper of the vehicle setting out that the vehicle was detected speeding and that the driver of the vehicle needs to be identified.
If the driver was you, you can respond directly to the letter with how you would like to proceed (pleading guilty or not guilty to the speeding offence) and, if applicable, agreeing to attend a driver education course or to pay a speeding fine.
If someone else was the driver, you must fill out the Section 172 paperwork (included with the Notice of Intended Prosecution) with details of that driver and a new Notice will accordingly be issued to them. If the driver was someone else, it is important that you do not hand your Notice over to them; they must fill out the Notice that is sent to them directly otherwise you will be processed as the driver and not them.