Thanks Inge. It's a real beauty. I've seen one other like it which I think was also 3.5" gauge and may have also come from BL. Was talking with a friend the other day who used to go to the Steam Age shop in London. I restored a 3.5" gauge GNR Atlantic from about the same period. Just a tidbit of info--Patrick Stirling, designer of this loco, was the son of Robert Stirling who invented the hot air engine.
If the other one you seen was another forum members, this may be the same one