wrote:
[...]
The term "Tube" goes back to the earliest days of deep-level tunnels.
Wasn't
the Central London Railway (now the Central Line) dubbed "The Tuppenny
Tube"
soon after opening in 1900?

It was - the company promoted themselves as such (dunno if they actually
first came up with that phrase though) - but my comments were more in terms
of when the term 'Tube' became a popularly used expression to describe the
whole system, whether deep-level tube or sub-surface lines.