Hi
This may be late, but if you have lost ALL power, look for the RCD, the big switch on your board, thats tripped out.
If however you are plugged into the mains on a site it could be the trip on supply bollard or the trip in the supply where ever it's plugged in.
A standard vac will not overload any circuit in the van, they are rates up to about 1250 watts, which when translated into amps at 240 volt will be 5.2 amps, the ring main is normaly rated at 16amp.
Should you have had on at the same time another item, i.e heating / water heating / full sized kettle, then that is more than likely your problem, simply an over loaded circuit.
To stop thos happening again, calculate all all the power ratings of the appliances in the van, including heating and water heater in watts, divide by 240, this will give you a approximate current rating, simply do not cross the supply rating, most sites we have been to allow 16amp, but one or 2 anly allow 10amp, check the bollard for a rating or ask the warden.
We have tripped ours a rew times, through not paying attention or forgetting the heating was on, and we use a domestic kettle (it boils so much quicker)
I would suggest that you may want to consider a small multitester, that way you could find simple faults or overloads.
There are also some guide lines on the web site taht you couls download.
Best of luck, hope you find your problem