Depends on what your plans for the property are. If you are renovating, this external conduit to the switch doesn't look very nice. It is too close to the door opening, too. I personally would move it a little bit away from the door frame and would change that length of the architrave.
If you don't want to do this or as a temporary solution you can put a surface mounted box for the switch. It will stand proud of the wall and would fill the gap in the timber. May need a bead of decorators caulk around.
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