I haven't done this but I think it might work.
Start with the car on an even level surface and the top fixed in place. Think of it as putting the chassis in a baseline/neutral position.
First, remove the strike plate (the receiver part on the rear door jamb) completely.
Second, for the benefit of those who haven't loosened the door hinge screws yet, do so VERY carefully, noting that these screws have a big assed phillips/cross point head because they are dealing with a lot more torque than your average phillips head screw, and that you will need a big assed screwdriver to match the head so you don't strip out the mating surface of the screwhead. IIRC Eurosport UK carries
replacement screws with an allen head, probably a superior overall solution.
Third, loosen the door hinge fixing screws to the point where the hinges are clamped in place just so they can be grudgingly moved by exerting pressure on the door. Not sure exactly what that would be---I'm sure lots of trial and error would be involved in dialing this in just right.
I do know from personal experience that you do NOT want to try to adjust your door by loosening just one hinge. Doing this puts the hinges on separate axes and the result can be a maddening metallic groan from one hinge pin that no amount of lube will fix.
Fourth, now carefully close the door and see where it lands. Without the strike plate in play, the door will land where it wants to rather than where the strike plate wants to lever it.
Fifth, adjust and adjust and adjust until the door lands as best in can in the door opening. Even up your front and rear gaps, and see if you can get the bottom gap even with the sill. If you can, get the door skin and the front and rear fenders sitting flush, too. As mentioned by EricH, to correct a big "droop" you may need thin shims between one or both hinges and the front jamb.
Tighten the door hinge screws just a tad and check again. x 2 or 3 until they're good and tight.
Now roll up the window and carefully shut the door to see what that looks like. Hopefully the door glass and opening seal meet nicely.
Next, put the strike plate back, snug it up a bit, and let the closing of the door establish the strike plate in its place. Open the door, snug up the strike plate some more, close and check fit. When done, tighten the strike plate screws to spec.