I would have expected the vans circuit breakers to trip if the circuits were overloaded and the hook up if the van was exceeding the supply there. The sites ones can trip though, if too many people are near the individual hook up limits.
Was the problem reported to the site staff and investigated to see if it was their system?
If the other pitches were getting power, then it might be your hook up cable, I would check that for damage and for any loose connection in the plugs, but otherwise I would get an engineer to look at the caravan.