Cracked it!
Used a Flat Bladed Precision Screwdriver, the trick is not to try to lever up the scre as well.
The cap has no retaining lugs, it just an interference fit, so you need to just push the screwdriver only the lsightest amount to get it to pop off.
I will post a pic of the unside of the cap in the next few days so that it helps other members if they are trying to remove also.