Well, in the absence of any advice this is what I did (so that others may benefit).
1. With the door lock in situ remove the door seal from the door frame.
2. Loosen all the door bolts, slacken the hinge pins off too.
3. Remove striker
4. Close door, lift and push until it sits absolutely flush with the rest of the body panels and there is an even gap all round. Observe position of hinges and how much lift in which direction you need to give the door.
5. With remarkable skill, imagination and handful of ingenuity place a ring spanner on the uppermost outer door bolt nut (inside), close door and lift into position then tighten the corresponding bolt.
6. Repeat with adjacent nut & bolt (open door, reposition spanner, close door, lift and tighten).
7. Work the way down the door hinges, leaving the hinge pins slack and inner door bolts loose.
8. Once the hinges are tight, refit the striker plate and shims, loosely, climb inside and through trial, error and observation find a point where the door lock will fully close and the latch will click through twice.
9. Refit the door seal.
10 Try the door again to ensure the seal is not preventing the door from closing.
11. Tighten the inner door bolts (same process, ring spanner inside, shut door and tighten).
12. Finally, adjust the hinge pins with the door shut, open the door and see if there is wiggle, repeat until wiggle gone.
Note: It's a helluva lot easier if there are two of you! Not having the door seal in gives a tiny bit more adjustment on the striker too. It can be gently tapped into place once the striker has been tightened. Also, the rubber bush that sits on top of the striker plate may need some adjustment to allow the lock to travel in further.