Mains Circuit Tripping - any advice please

Could anyone please help me?  I have just returned from a weeks holiday in the caravan and for some reason the MCB kept tripping out, it was the one protecting the plug sockets.  This has never happened previouly.  It reset straight away , but would trip again sometimes after several minutes or after several hours.

Has anyone else experienced this and if so any solutions would be greatly appreciated.

The caravan is a Coachman 500/5   Thanks