Didn't really expect much from DrivingUk but honestly the amount of downvotes shocked me. God forbid people go out at night dressed normally without full on high vis.
Reddit Link: https://www.reddit.com/r/drivingUK/comments/1r8fkfo/comment/o65j18p/
I wear a helmet while biking. It's saved me from a head injury once so far, in an accident that had nothing to do with being hit by a car.
I don't think it should be legally required, though, because avoiding discouraging people from cycling at all is more important for safety and health in aggregate.
(I was riding along at relatively low speed, looking up at some scenery, and hit the longitudinal edge of a cockeyed metal plate in the road in just the wrong way such that it pushed my wheel sideways and made me fall over.)