usually it's not. The standard wording is 'we strongly advise'. That's to get the organisers insurers off the hook........Looking to enter my first 100k next spring. I don't wear a helmet and only want one for occasional wear (sounds like a wedding) so will the cheap £15 "Bell" model from Asda do the job?...it is obviously a requirement of mass participation events that a helmet is worn....
Since they are all tested to the same measly EN standard (Specialized excepted) it will protect or not protect as well as any other.
Cos they can. clear enough for you?How can group rides insist on people wearing helmets when it is not a legal requirement? I would take offence to that as I don't ever wear one.