Don't be fooled by the sparky (electrician).
Tell him to get off his butt and fix the problem, as you could have an electrical fire anytime, worst thing to happen if everybody is asleep.
If the sparky insists the problem is the RCD then do the following:
Take the RCD back to where it was purchased and ask for an exchange or get it tested.
If the problem persists thereafter then report the sparky to:
www.electricalsafetycouncil.org.uk
Regards
Harry
October 2006