I'm not sure how you do it over in the U.K., but on this side of the Atlantic if the club books an artist they usually have a contract that stipulates what the artist needs or will be bringing. Clubs normally provide the sound system.   I am guessing Peter that YOU are the one who feels it is inappropriate since it doesn't appear that the venue or it's organizers did anything to prevent this supposed "inappropriate" amplification.   I'm guessing that it probably boils down to a matter of taste.