"R.C. Payne" wrote

But given that 1/- is exactly one twentieth of a pound, and 2/- is
exactly a tenth, it makes sense that the replacement coin for the same
value, ie 5p and 10p be essentially the same coin, and by extention,
that the old coins remain in circulation. I certainly enjoyed getting
change with a king's rather than queen's head on it. I never happened
upon any older than about 1950, but still...

Until the 1960s it was not that unusual to get 19th century coins - with
Queen Victoria's head - usually pennies but very occasionally silver coins.
Until the new small 5p came in shillings dating back to 1816 were legal
tender, though I don't think I ever saw George III, George IV, or William
III examples. There were also occasional press stories of silver groats
(4d - not Maundy examples) surfacing, being mistaken for silver 3d or
sixpences.

Peter