Is it illegal to park on zig-zag lines outside schools?

Yellow zig-zag lines on the road are most often seen outside schools, yet many motorists are still unsure as to what they mean.
Can you park on single or double yellow lines?

Parking on yellow lines explained

Yellow lines mark the edges of roads where local authorities don't want you to park, but what is the law on the subject?
The Sunday Times Driving Placeholder

Letters of the week, October 19

This week: Guy Martin's impossibly fast Volvo, refuelling mishaps and the lawlessness of Welwyn Garden City
The Sunday Times Driving Placeholder

News: Council paints double yellow lines on 3ft wide...

It’s barely 3ft wide and far too small for even the tiny Smart city car but a stretch of tarmac in one north London street has still been painted...
The Sunday Times Driving Placeholder

News: Parking signs to be scrapped — but no escaping...

Motorists will find it harder to challenge parking fines in future under new government proposals.