Another thing you can try yourself is to try and trigger the RCD with the washing machine unplugged / isolated.
If you plug in a fan heater or hair dryer to a circuit protected by the same RCD, and the RCD trips then it proves the issue is elsewhere and the washing machine just happens to be the thing sending current through the fault to cause a trip. If the RCD doesn't trip then it's pointing to the appliance.
If you call a decent sparks in, then within hour 1 they should be able to discover whether the problem is with fixed wiring (and if so, which circuit) or the appliance.