I think this explains the principle CLICKY THING

I personally find these offensive and very exploitative of the worker.

I suspect that they are used as a way of manipulating the unemployment figures, as technically a person is employed.

Perhaps my understanding of this is wrong and I am barking up a gum tree so to speak, but it would seem to me that for the individual it carries few if any benefits, for the employer they can give those on these contracts work on an ad hoc basis which might work for those who do it for a little bit extra here and there and not depending upon it. Another thought that crossed my mind is if people are signed up to zero hours contracts, technically, are they off the job seekers list and helping to make the unemployment figures look better?