David Lee wrote:

BTW does anyone happen to know what the Sheffield supply voltage was back in
the 1950s - I remember a van coming down the street and engineers converting
all our appliances to work on 240V AC but for the life of me I can't
remember what it was before that.

I don't know about Sheffield, but We had 200V until about 1960. Con.
Ed. were still supplying a few industrial customers in New York with
d.c. in the 1990s. I believe they had to give something like 40 years
notice to terminate the service.