https://www.economie.gouv.fr/files/files/directions_services...INSTRUCTION CODIFICATRICE etc
meant for civil servants employed by the French Ministry of Finance
Can't copy-paste - won't work.
If you go through the document you will find
1 -- that none of "ordonnateur", "agent comptable", "comptables secondaires", "agent comptable principal" nor "comptables d’ordre" are used interchangeably - they are distinct types of civil servants / different roles in the execution of the budget;
2 -- that
"comptables d’ordre" are ONLY accountants - they have no authority whatsoever to give any "order to pay mr XYZ" to absolutely no one (=> they are not any kind of "ordonnateur") - all they do is accounting.
Right now, I have no idea how this subspecies of accountants working for a public authority would be called in UK, but they are definitely **NOT** any kind of "authorising officers / ordonnateurs".
This one might give some useful clues:
L'agent comptable, comptable public ....
https://www.institutfrancais.com/fr/agence-comptable+
The public accounting officer ...
https://www.institutfrancais.com/en/the-accounting-agency