Humps are now usually marked with a single line either side at an angle to the kerb. Is this what roz means by zigzags? If so, then there is no problem parking on them. It's only the zigzags at pedestrian crossings that stop parking - they are totally different. I can't find any reference to the hump markings but you can find the details of zigzags in The Traffic Signs General Regulations 2002. Look in the section on Road Markings. This document makes fascinating reading for those without a life!