Yup... allowance for postage.
Q, I have been flashed by a speed camera, what happens next, 14 Day Rule.
The Police have 14 days to send you a Notice of Intended Prosecution (NIP). They also get an allowance of a couple of days for the post to deliver it. So if its more than 17 days since you were flashed they are too late to prosecute you, unless you were driving a company car, hire car or someone elses car. In these circumstances they are allowed more time to track you down.