I'd like to thank you for this suggestion, there were various steps necessary including WD40, and each fitting had to be removed from the ceiling causing minor damage but ultimately this little tool is what made the difference. Using a screwdriver I was able to twist the notch on the bezel...
Most are in the hallway upstairs and various other rooms too. Re your second question, the one in the images has now been opened by a handyman using a wrench. Next job is to see if the rest can be opened with the same method without having to remove them from the ceiling!
Just moved into a house which has downlights everywhere. We are gradually swapping over to LED but have encountered one type of fitting which has everyone stumped as to how to remove the bulb, including an electrician friend! Having given up trying to twist/turn the bulb and its surround, we...