Probably designed in the first place to stop people singing songs in taverns in support of the rebellious colonials in America, or Bonnie Princ Charlie or some other 18th century priority...

Essentially, it's there because it's there because it's there - and nobody has made sufficient fuss about it to bring about a change. Inertia.

If anyone reads through the threads about this (which I listed with links on 20 August at 7.21 on this thread, with a couple added in later), especially with the links to Hansard and so on and so forth - they'll know far more about this than any councillor or MP or Minister they'll come up against. So you'll win the arguments, but that's not good enough to win the war.

If keeping the law this way can be made a nuisance, I imagine it'll change, because it's not really to anybody's positive advantage to keep it the way it is. And if it ever gets into a court which has to take Human Rights into consideration, the current law hasn't a chance.