And while you're out checking the lines in the middle of the road...
If you come across a parking bay with signs like
this (660.6) they must have lines on the same side of the road as the sign which are drawn to one of the following diagrams:
1028.4
1032
1033
There must not be a legend on the bay (eg. it must not say "DOCTOR" or "PERMIT HOLDERS ONLY" or any other permitted variations.)
Where I live they recently put up a residents parking scheme and I noticed that the lines are wrong. I checked around the town and found that most of them are wrong. They have double white lines at one end and single white lines at the other (a cross between 1028.4 and 1032) which is an easy way to tell that it is invalid.
It the lines are wrong the sign is invalid. If the sign is invalid they can't enforce it.
Info from
The Traffic Signs Regulations and General Directions 2002.