What do those zigzag lines in the roads mean?

Zigzag lines are painted on the street either side of a Pedestrian/Zebra crossing and outside Schools for example. It is an offence to stop on the lines and you will be issued with an immediate fine for doing so as well as a 3 point penalty on your driving licence.

The idea behind it is to allow driver's maximum view of person's crossing at that point.

It might be worth adding-----

If you do not accept the Fixed Penalty Notice and opt to go for trial at a magistrates court, the maximum fine if found guilty is £1000.

You are not allowed to 1) stop ahead of a vehicle already stationary on a zebra crossing for the purpose of letting someone cross and 2) nor are you allowed to overtake a moving vehicle going the same direction on a zebra crossing.

I do believe local buses services--not tour or excursion buses/coaches--are allowed to stop on the far side of a zebra crossing on the zig zag lines, for the purpose of picking up and setting down of passengers.