Pat, if you're still around, there is a mixed dance night including French Jive or Modern Jive (they seem unable to decide which) at Jongleurs in Oxford, UK, which I understand is reasonably close to London (90 minutes by coach, I was told), but only an option if you're desperate. I was unable to verify whether there would be French people there, though, and whereas the first time, it costs £5, subsequently you pay only £1, which seems suspicious to say the least, I think.

Happy jiving!