@MarkBatch: Typically the door lock will remain active when the machine detects that there is water in the drum. Although I understand that you may have tried this already, please follow the steps in the link below to drain the water via the emergency drain hose.
You will also need the machine to be powered on, which I appreciate may not be possible. Do you have access to another power outlet that you can try to see if you're able to restore power to the device?
@MarkBatch: If you are unable to power on the machine, then an engineer's inspection is recommended in order to get this back to working order for you. If you are based in the UK then please follow the link below, click on 'Home Appliances' and follow the on-screen instructions to arrange an inspection via a Service Centre near you.
