The reason I've been putting off tackling the struts is that its described as a pig of a job, with seats out, panel off to get access to the retaining nuts.
A US forum gives the procedure as:
There are 2 bolts on either side of the hatch and 2 nuts on each side where the strut end connects to the body. You'll need to either remove that panel or gently pry it open to get a ratchet in there.
How to do, first take the rear seats out, then take the side trunk plastic panels and rear side speaker panels out, then the rear side window panels out, that should give you access to that mounting area. make sure you dont pull too hard on the panels which means, there a bolt there somewhere. this job should take 2~3 hrs if you know your way around the car or 3~5 hrs if your new at it.... it a bitch, I know...
There is another remedy that is often employed and that is to bend the rod back toward the tailgate. This has been reported as a semi-permanent fix to degassed struts.
Lastly, I did contact SGS Engineering Solutions who do struts. For about £80 plus shipping they will refurbish or exchange your struts. Then need to recover the fixings. The tailgate is one big piece of metal though and the thought of changing both struts without even one strut providing assistance holding it up was too much. Maybe I'll just go bent rod?