I have spoken to Stannah, who are not very helpful, quoting Elphin safety/ the world will stop spinning etc., they will remove for a fee and reinstall for a fee etc. My original assumption was that the chair could be dropped onto the track anywhere, then just have some sort of bottom retaining clamp fitted. This time, I am thinking - remove one of the two sections of track, and run the chair off the end of the track. Now I want to change the stair carpet and the lower part of the brackets are fixed to the stairs through the carpet, each bracket has four large screws into the wood. It wasn't an easy job to lift it and move it across and refit due to the sheer weight of it, but I couldn't see an easy way to lift the chair off the track at the time.
Then I disconnected the rail from the brackets and lifted the two rail sections (straight run up the stairs) over with the chair still attached leaving the lower brackets in place. OK, I have already done this the hard way, just a few weeks ago to decorate the stairs.