There are persistent myths that parking for short amounts of time don’t count. Obviously, the less time you spend parked somewhere you shouldn’t, the less likely you are to be caught there, but it’s no guarantee.
Where loading is allowed, Civil Enforcement Officers/Parking Attendants/Traffic Wardens will usually observe to see if they can see any loading happening. Five minutes is common, but councils set their own policies on this. The longer they observe, the more persuasive their evidence is (and the more evidence they are likely to expect from you), but they may set shorter observation times, especially where observation periods are seen to be being abused.
In March 2015, then communities minister Eric Pickles announced a “ten-minute grace period” before parking penalties could be imposed, but this was poorly thought-through, poorly communicated, and poorly understood by many of the public, especially those who only read the headlines, and mistakenly believed it allowed ten-minutes free parking anywhere. The grace period only applies to staying longer than is allowed somewhere where parking is permitted – so in limited waiting bays, and when pay and display tickets or meters have expired.
There is also a surprisingly common belief that single yellow lines allow parking for half an hour. I have no idea where this mistaken belief comes from, but a yellow line indicates that parking is not allowed during times shown on a nearby sign.