Republican protesters arrested at King Charles proclamations
theguardian.com
theguardian.com
In other words, suppression of dissenting speech by the state. Something that seems more like a dictatorship than a modern democracy.
Always has been.
Personally I don't think this was official policy, just over-zealous individual police-persons.
In the case of the monarchy, there is probably an element of insecurity as well as a general acknowledgment that they'll be criticized constantly and can't let it bother them.