Some do not seem to clued up about zebra crossings .As I said they must have belisha beacons before they can be considered a legal crossing.
And yes on a proper crossing as soon as a pedestrian steps foot onto the crossing you are required by law to stop.
Any decent professional driver would stop if pedestrians were waiting but from what I see most are in to much of a hurry these days.
Last but not least us professionals know Pedestrians have right of way in most situations.