OK, so my badges finally arrived.
Before removing the grille I thought I would (opportunistically!) give the existing badge a light tug (counter clockwise), putting my forefinger and thumb between the 'V' and 'W'. I immediately felt one of my clips pop out!
So I carried on gently wiggling until all clips released and I was able to remove the badge.
My replacement 'badge' was actually just a replacement cover! So I had to carefully remove the chrome VW badge 'face' from the unit (for which I used flat-head screwdriver to undo all the clips). This part of the job was a bit of an arse, but I managed to get it off in the end without damaging it too much. I then fixed the black badge 'cover' in place of the chrome and put the badge back into the grill (point the 'V' at 10 o'clock and then rotate clockwise to upright position).
Did the trick...
I really should take some better pictures!