For some reason its always the left rear door which does this, and the bolted-in window frame holds it out of shape. The trick is to release all the bolts holding the frame in, which allows the door skin to relax, and then tighten them up again.
Often this alone will allow it to sit flush again. In some cases, such as Andrews, it needs the frame removing and the door skin tweaking back in to shape (by applying a knee at the bottom corner and some light leverage from she who ate all the pies at the top), checking it fits flush with the body, and then refitting the frame
