Just to say many thanks to Chris Rowe, who sent me an e-mail with further information about the Waddington's piano factory - he has managed to unearth some old pictures and postcards.
This is the front of the postcard, showing the Waddington's factory amongst a collage of other buildings which are in the Minster and Duncombe Place areas nearby.
The back of the postcard lists Waddington's branches at the time.
This photo shows the Waddington's piano factory behind the Star Inn in Stonegate - 7 windows side-to-side and a remarkable 6 storeys. I presume this photo was taken some time in the early 20th century.
Thanks once again to Chris Rowe for this fascinating information.