Intermittent faults are the worst - but that's not a reason for an electrician to have charged you, but left you no better off.
If it is an earth leakage breaker that's tripping, the live to neutral (normal) power consumption of any appliance is irrelevant.
And if the ring main is tripping, I'm not sure why you think the cause might be in the bedroom.
Your mate will need some patience and a process of elimination but hopefully he will cure it.
(I'd start by completely isolating any connected washing machine).
I have as I thought the washer might be touching a brass pipe, I made sure when the electrician came everything Inc the cooker was unplugged to save time and false suggestion.
I've still replaced every lead in the bungalow against my better judgement despite them testing ok.
The bedroom has me suspicious as it's tripped when I've plugged different things in and I've had a few appliances go faulty in there, all could be coincidence.
What's strange is after the new RCD was replaced it still tripped off that night without a single thing plugged in, it hasn't since.
I know the electrician was scratching his head when it tripped without anything plugged in as he was stood there as everything tested ok although to my suspicion the earth was a tad high but still within tollarence.
My friend suggested more drastic action as in his words it's definitely happening despite counter indication from the consumer box and sockets.
He's coming back with his friend to split the sockets.
I've been using the electric in the interim and it hasn't tripped since.