Unplug the appliance.
Take the panel on the rear off.
At the bottom rear of the tub you'll see the heater terminals.
Disconnect the wires to the element (not the thin ones to a tiny plug).
Tie them back out of the way.
Try the machine, does it still trip?
If it does, reconnect the heater and unplug the motor.
Remember to unplug before working on the machine and wait 10 minutes after unplugging before touching anything.
Removed the heater wires and with the door open the machine switches on. however close the front door and it trips.
the same occurs with the motor disconnected, with both disconnected and with both reconnected.
So long as the door is open, the power stays on.
OK, it's possible the door lock is the cause of the problem.
Unfortunately, it's a difficult one to prove.
Take the door seal off of the front panel and take the door lock out through the port hole.
See if there's any obvious damage to it.