It used to be a rule that a parking ticket had to be stuck on your windscreen or handed to you as the driver for it to be valid. If you drove away before either of these took place any ticket issued afterwards was not valid.
The anti-motorist organisation Transport for London decided to change this a couple of years ago. Regulation 10 of the Traffic Management Act 2004 states that in "drive away" cases an enforcement authority could issue a ticket by post if the parking warden had started to prepare or had printed out the ticket at street level. This is not only wrong, but a rather silly and largely unworkable regulation.
The drive away rule was right in principle since authorities did away with any meaningful observation time before a ticket was issued. But besides this, most enforcement authorities have decided not to use Regulation 10 because in most cases it's difficult to prove that a contravention has occurred, and because of all the caveats and exemptions that went with Regulation 10. So Transport for London have overstepped the mark with this one and Regulation 10 is a bad rule and should be repealed.
Why is this idea important?
Because it's right in principle that where there is on-street enforcement a parking ticket has to be served at street level for it to be valid – despite Transport for London's evident annoyance that too many motorists had been "getting away with it" by driving off before this could be done.
Also, because Regulation 10 is largely unworkable and not used by most authorities. Most parking ticket appeals where Regulation 10 was involved have been upheld, and it is therefore a waste of time and money for enforcement authorities to pursue alleged contraventions in these circumstances.