"The purpose of the legislation is primarily to ensure public safety (eg numbers attending) or noise dosen't become a nuisance." Surely this is a nonsense as both these matters are covered by other laws?

I think the thing is that back in the 18th century there weren't the other laws. But in bringing in new laws about these things, noone ever seems to have thought it worth looking at the old ones - and it's when the two work together that you get this kind of nonsense.