In these circumstances :
Under 18, or under 19 and in full-time education
Receiving low income benefits, or you're under 20 and a dependant of someone receiving low income benefits
In a previous life I investigated NHS dentists and later was involved in chasing people who had incorrectly claimed free NHS dental treatment.
Soon it may come to this:
https://www.youtube.com/watch?v=IMhGUhSNKmQ