-try unplugging all sockets on that socket circuit, dont forget to switch off all switched fuse spurs, that may also connected to that circuit.
-switching of at the switches will not disconect to neutral, so you will have to unplug all the plugs.
-switch the mcb to on & plug in all of the plugs one at a time, to see which appliance in reponsible for causing rcd trip.
-failing that call an electrican to find your fault, which could be either a live - earth fault or neutral - earth fault somewhere within that circuit!
best of luck
Faulty Fixer, November 2010