That is a good quick fix suggestion especially if exposed to the elements but in fact, and perhaps I should have included this in the original post, that this old wooden door is protected from the rain by an exterior aluminium porch door. But since that door is single glazed aluminium it does...
My front door is in a frame that has bowed (subsidence from years ago) with a major gap on the hinge side which starts at 4mm (acceptable) at the very top and gets up to 16mm in the centre and then returns to about 12mm right at the floor. The door has two window lights either side so I don't...