In message , Jeff writes

FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

Well perhaps not 'always'. FM was not allowed prior to about 1952.

In those days, some AM transmissions had quite a lot of FM on them!

10m FM works well using modified CB sets (2.5kHz deviation and 10kHz
channel spacing). It slope fairly well using my Eton SW receiver with
the AM filter switched to 'narrow'.
--
Ian