So, bearing in mind that coughs and splatters is not a particularly technical term lol (as in does that mean fires, fails to fire, turns over quickly or slowly, fires on some but not all cylinders, spits back etc etc etc).
So, if we start again, and trying to be EXACT. Are you saying that nothing at all happens if you try to start it purely from turning the key (which may still not mean its a battery problem), but that when you use jump leads, the van's starter motor at least turns over (which will rule out three possible faults at least, such as jammed starter, faulty solenoid, and unearthed starter motor/engine, but does still leave faulty ignition circuit as a possibility)
most of the time it was starting in the morning , but it is definately worse when there is a cold snap.when i turned the key this morning it turned over a couple of times and then it sounded like the battery was getting weaker and then just click.