You lot was conquered by the Normans innit. Who spoke French. So there's a totally reasonable association of Frenchness with poshness in Britain.
It's more complicated than that. French surnames like Dujardin and Dupont aren't at all aristratic; they're emphatically plebeian in origin. Nobody with a surname like that can trace direct (and "legitimate") male line descent back to a Norman aristo. On the other hand, if the family surname survived a few centuries in Britain without being anglicised (rather than tracing back to a more recent arrival), the original immigrant family probably climbed a bit up the social ladder, before or after they arrived here. Demlin? French immigrants who stayed pleb. De Moleyns? Posh.
It's more complicated than that. French surnames like Dujardin and Dupont aren't at all aristratic; they're emphatically plebeian in origin. Nobody with a surname like that can trace direct (and "legitimate") male line descent back to a Norman aristo. On the other hand, if the family surname survived a few centuries in Britain without being anglicised (rather than tracing back to a more recent arrival), the original immigrant family probably climbed a bit up the social ladder, before or after they arrived here. Demlin? French immigrants who stayed pleb. De Moleyns? Posh.