Why does pump shut off when trying to fill car up?

Years ago a friend had a cherokee chief jeep, we drove it to Scotland from kent a few times, all I remember about those trips was the constant stopping to put fuel in it because of the almost 6litre V8 on an auto box drank fuel, it wasn't even nice to dive, it had the awful handling of a knackered range rover coupled with the acceleration of a diesel land-rover, it's most memorable feature was a pedal that was the hand brake, it had a button or lever to release it but if you'd applied it with muddy boots on releasing it launched mud into your face. We had a diesel corsa, I hated that car because it represented everything bad about cars, however I went to look a a 4kw diesel generator and decided to buy it, rather than drive home and return with something equally impracticable but in the other extreme we decided to measure it and the space in the car, it fitted but had to be on it's side, flushed with the success of this (and the stench of diesel) a week later we went to collect a much heavier diesel welder, it caused serious handling problems that put an end to carrying stuff in it.......the next purchase was a 6ft wide mowing deck for a tractor, I strapped that to the roof and got showered in glass from what used to be a sunroof, sadly I don't have anything sensible, it's either an inappropriate car or a unimog.