Sorted.... the angle / access is a bitch.... But the key was working out what needed twisting....
There are some stand-up metal "hooks" - but these are fixed in place, and this is what the bulb holder twists into....
So, the trick was to grab and twist the black bulb holder... Twisting anti-clockwise... but remembering you are looking back on yourself.... so kind of upside down...
Just to confirm, the mole grips comment above was tongue in cheek.... what I used was an old rag (t-shirt), and warm hands having just had a warming coffee... and knowing what to twist and in which direction is the key.... Gloves if available.... would have likely worked just as well...
Having removed it, the bulb really didn't want to come out of the holder, so a flat bladed screwdriver to prise it out gently helped....
Replacing is the opposite of removal, but so much quicker....
Thanks for the support / encouragement...
Malcolm