I have been out to a job where the rcd has tripped and the house owner has switched the rcd back on and no supply has been restored, this was because the switch needed switching completely down before flicking it back up.
I do not know if the rcd switch in your van is of the same type but it may be worth an attempt.
Also, I recently attended a customer who had no socket supply, even though supply was getting to the consumer unit and to the circuit breaker but, as it turned out, the breaker was faulty and had to be turned on and off several times before power was restored to the sockets.
If above does not work I would unplug supply to van, take off the cover to the consumer unit, check with a continuity meter that the socket circuit breaker has continuity between both ends of the breaker when in the on position.
I would also check the main incoming isolator (or RCD)for continuity.
If so chances are the breakers are ok.
Replace unit cover and plug in and switch on the van supply, ensure breakers are in the on position, and test socket outlets by means of a tested table lamp.
If still not working then your next course of action would be live testing, of which should not be messed with unless you feel competent to do so.