OP, also see this:
https://assets.publishing.service.gov.uk/me...ad-markings.pdfWaiting restrictions indicated by yellow lines apply to the carriageway, pavement and verge. You
may stop to load or unload (unless there are also loading restrictions as described below) or while passengers board or alight. Double yellow lines mean no waiting at any time, unless there are signs that specifically indicate seasonal restrictions. The times at which the restrictions apply for other road markings are shown on nearby plates or on entry signs to controlled parking zones. If no days are shown on the signs, the restrictions are in force every day including Sundays and Bank Holidays.
You should know this as you hold a licence.
Qu. If I park on a yellow line (which did not have an associated loading restriction), whether single or double, could I get issued with a PCN?
Ans. Of course.
Why?
Because if you are not with the vehicle or there are no obvious signs of loading/unloading(which also means delivering and collecting) then a CEO would presume the worst, and why not?
If this situation occurred you would need to prove you were delivering etc. in order to be able to claim the exemption.
Moral: get everything in writing where possible e.g. delivery instructions, delivery notes AND as we're in the mobile phone era take YOUR OWN PHOTOS of goods you unload or collect. Create your own album, it would take a few seconds and provided the activity was on yellow lines you could discard after a day.