Thanks for comment. I managed to use the shortened copper insert tube and undo the return locking screw and all is working perfectly. No need for a new valve.
I am trying to replace a radiator after decorating. It is a microbore system with a return valve and pipe. The insertion tube became loose and I had to shorten it at the return end. I then pushed the tube back but it seemed loose. In addition when I did replace the radiator the return screw...