Umberto Eco gave a pretty well-reasoned definition of Facism, and I think it's pretty straightforward to apply this definition to the situation in London (and DHH's commentary thereon): https://en.wikipedia.org/wiki/Ur-Fascism

Just look up Tommy Robinson.

> He was a member of the British National Party (BNP), a British fascist political party. [1]

A march in honor of Tommy Robinson, who is a fascist. Not sure what else to tell you.

[1] https://en.wikipedia.org/wiki/Tommy_Robinson