Thanks - sorry about that!
I like the indigo.server.log trick - must use that more often. See attachment (too big to post as text on forum page really)
FYI I've just rebooted and done another MQTT cut and paste and it differs from the attachment:
23/04/2020, 23:33:27 indigo/light/1121785643/config q0 r0 i0 (518) #5 (taken just before post)
"name": "Dining Room Desk Light", "deviceId": "1121785643", "model": "Mulitlevel Switch", "address": "9", "states": { "brightnessLevel": "31", "onOffState": "True" } }, "capabilities": { "supportsAllLightsOnOff": "True", "supportsAllOff": "True", "supportsColor": "True", "supportsRGB": "True", "supportsRGBandWhiteSimultaneously": "True", "supportsStatusRequest": "True", "supportsTwoWhiteLevels": "True", "supportsTwoWhiteLevelsSimultaneously": "True", "supportsWhite": "True", "supportsWhiteTemperature": "True" } }