Question

The power sockets (2) in my motorhome cut out, and stay off for varying lengths of time. The fuses are not blowing, and the main trip switches stay on. The fridge (separate circuit) stays on, so it's not a problem with the EHU supply

Answer

This would point to a faulty Micro Circuit Breaker in the Consumer Unit. This would normally be the 10 amp or 16 amp unit.