This might shed some light https://en.wikipedia.org/wiki/Comptoir_national_d%27escompte_de_Paris They opened a branch in London, England in 1867, so this is possibly a commercial overprint but perhaps someone else has better knowledge.
Yes, it's a commercial overprint. Here's a nice page with different examples from the bank: https://commercialoverprints.com/comptoir-descompte-de-paris/
Unable to classify this common (Scott's SC #89) Queen Victoria issue with French overprint. Need history and value of stamp if known.
re: Great Britain Q. Victoria O.P.??
#89) Queen Victoria issue with French overprint. Need history and value of stamp if known.
