What do these zigzag lines at pedestrian crossings mean?

Explanation: The approach to, and exit from, a pedestrian crossing is marked with zigzag lines. You mustn't park on them or overtake the leading vehicle when approaching the crossing. Parking here would block the view for pedestrians and approaching traffic.

Category: Road and traffic signs

References: The Official DVSA Guide to Riding: Section 8, Highway Code: Rule 191, Know Your Traffic Signs: Page 122