Villan.
think how europeanised, England has become since the 1950s,everything changes,and changes much quicker than is often predicted and in this computer age will change even quicker.
professional folksingers are lowerpaid than catering staff,why the Dickens shouldnt they be tipped,if the member of the audience has enjoyed the evening,and does so voluntarily.
as an organiser,you can not prevent someone tipping an artist.,any more than you can stop them buying a performer a beer, or a cup of coffee or a soft drink.