1. If the tap is on a microswitched system, the microswitch may be jammed in the closed position. This means that it will not switch off so the pump will keep running. Check the actuating cam and, with the pump off at the main switch, put your (or Robin's) ear close to the switch and operate the tap. You should hear a distinct "click" when turning the tap on and another when turning the tap off. I cannot remember what type of tap you have on your caravan. If it is the Whale separate hot and cold type, the tap unit comes out by undoing the four screws holding it down the the work top and lifting it up. This will enable you to get at the microswitches. Operate the tap and listen. The microswitches are held on to two little plastic pegs by a plastic clip and are easy to replace if necessary. Just remember which tags the wires went on to. If the tap is the all-in-one mixer tap with the red and blue disk on the lift up lever, prise the red and blue disc up with a small screwdriver, undo the screw and the tap lever will lift off. Be gentle in case the operating cam pops out unexpectedly. Note which way the cam came out so that it can be put back in correctly. Check the switches and replace if necessary.
General comment. If you have access to a multimeter, put it on OHMS setting and check continuity across the terminals on the switch with the little button pushed in or when released. You should have a reading then no reading when the switch actuator is pressed or the other way round. Some microswitches are dual purpose, i.e.normally closed and open when operated and normally open and closed when operated so if you use this method, you may have to check both ways. Of course, you have to mark which terminals the wires were attached to so that you can put them on the correct way again.
2. If you have a pressure switch system there are a further two possibilities. 2.1 The pressure switch is set at too high a pressure, hence the pump is having to stay on to try to get the pressure up to a level where it will switch off. If this is the case, turn the pressure adjuster on the top of the switch anticlockwise until it switches off. I would guess that the problem lies in this area. 2.2 If you are in the pressure switch scenario, it is possible that there is a leak in the delivery side of the system. This would stop the system getting up to pressure and the pump would stay on. I would look at the non-return valve just where the water comes in from outside. Sometimes they get stuck after a period of being left dry or a piece of grit or whatever is stuck in the valve making it stay open. Failing that, it is a case of running the pump and seeing if there is a leak in the system, possible all that is needed is a quarter turn on a Jubilee clip somewhere.
That's all I can think of at a distance. Unless some has other ideas!
Thank you Roy for all your time and effert on this write up for me i will show this to rob and let you know how we get on. We have a mixer taps and one in the bathroom which is also a mixer tap do we have to check both taps?
Hope that I have been of some help. Since we don't know which tap is causing the problem, I would suggest that you check them one at a time. Inevitably it will be the last one which is the culprit. You don't say which tap you were using when the problem manifested itself. It may help to go round them one at time and see if you can replicate the problem. That way you may be able to pinpoint which one is being naughty. Let me know how you get on by PM if you can make the time.