So here's the story. Dynamo bearings were a little suspect (fore and aft play) apart from that charging fine.
Changed bearings and then fitted to car. No bearing noise but not charging.
Checked wiring and light switch, charge light still on.
Changed regulator for new Bosch unit, charge light still on
Polarised dynamo. Dynamo spins when you add power from battery.
Charge light still on
Polarised dynamo again.
Charge light still on.
Checked battery voltage both with engine running and engine off (just over 6 volts so not charging)
In the back of my mind I know the dynamo has failed but does anyone have anything else I can try.