David of Broadway wrote:

UK-based vending machines, by and large, do not recognize the existence
of non-chip-and-PIN cards. (There are some exceptions. My card was
accepted on the first try at the leftmost vending machine at Golders
Green two weeks ago. I think the smaller machines may accept
non-chip-and-PIN cards.)

I can now also report success at the Louvre ticket machines. Seems like
it's possible to program a vending machine to accept non-chip-and-PIN
cards if desired.
--
David of Broadway