Don.
Threatening behaviour is still an offence in the UK Keith, as far as I know.
Of course it is.
It is not an issue of Freedom Of Speech.
We agree.

It is a very good example, for the reason that doing as you suggest would certainly cause panic and subsequent deaths and injuries, not related ro the fire.
The correct action is to very calmly and quietly ask patrons to leave, specifying which exits are safe to use.

No you silly man.
The person who discovers the fire may not know all that stuff and has a duty to tell as many as possible as quickly as possible.
Shouting fire is the correct immediate action.
It is certainly not an issue of free speech.