Will enforcement of licensing law spell the end of the traditional school formal?

Could the traditional school formal in hotels be at an end? Northern Ireland Hotels Federation has issued guidance to its members "that it is illegal for hotels to stage formal events that do not end by 9.30 pm and that persons under the age of 18 should not be at any social/family/entertainment event within the licensed area of an hotel after 9.00pm if no food is being served or 9.30 if a meal forms part of the event."