Thanks everyone.
The culprit was a 3mm T thread extension on the front of my camera. I took the "T block" off the front of the camera and then carefully managed to get the adapter off with pliers and rubber over the jaws. I want to prevent this again and do not want anything here that might ultimately end up in the camera eg. oily stuff.
Ken, it was your boot polish idea that I was trying to remember, thanks for that. Brown seems a neutral colour
Firstly though I might try the brasso and polish up the threads and see how that goes before I put it back together.
Thanks everyone.
Neale.