Interesting definition of "rare" as 16% admitted to it, so the real proportion is likely to be higher. Still if UK Universities admitted it was a problem, they might have to do more to deal with it. Having said that, can't see banning them will have that much effect. (Some) Essay mills are based outside the UK, you have new apps which advertise as giving complete answers to questions (again based outside the UK), ...
It would be interesting to see some form of timeline and see if things are getting worse.