There must be an ideological reason for the UK Police Helmet. I'm unsure what though.
So far im speculating on its Phallic shape, in terms of a male gender exposure of power. Especially since female officers seem to never wear them. They have no practical use. Except i assume as uniform, symbolic intimidation.
Im also speculating whether or not a method of augmenting the head in size. Similar to Animals, im thinking of some tropical birds, who spread their wings in a particular way in order to make themselves look bigger and special for mating or to scare off predators.