Its a long way to ship an RCM from England.
His best bet is to pull the RCM, remove the case and with the wires attached see if the relays are working properly and looking to see if the contacts are burnt. The relay may be operating correctly but the burnt contacts do not allow the passage of a current.
If another RCM from another car is available it would a smart idea to try it out in the car.
With the cost of shipping these days shipping thousands of miles gets a bit much.