What's the story behind those zigzag lines on British roads?

In the UK, the country with the safest roads in the world (IRTAD), there are currently five types of formal pedestrian crossings in use, these being Zebra, Pelican, Puffin, Toucan and Pegasus crossings. The most basic form of crossing is a pedestrian refuge, this is usually in the form of an island in the centre of the road, where pedestrians may wait in relative safety while vehicles pass on either side.

White zig-zag lines are used down both sides of the road and along the centre line of the road, both before and after the Zebra crossing, (See site for photo). These increase the warning to approaching drivers and also create a zone in which parking and overtaking (i.e. 'passing') are strictly forbidden.

http://www.driveandstayalive.com/articles%20and%20topics/pedestrians/pedestrian-crossings-and-crosswalks.htm