https://en.wikipedia.org/wiki/Oswald_Mosley#Post-war_politic...
There are quite a few things there (e.g. that he wanted laws against marrying someone of another race, that he saw himself as left wing, etc.) that I did not know, although id did know of his involvement in the Union Movement.
He was also a Conservative MP (later joining Labour)
The turnout was boosted by the murder of Charlie Kirk (yet another example of British people getting more involved in American causes than their own), and by some other things too I think, and although very big for a far right protest, it is far smaller than many causes have managed to organise over the years (anti-Iraq war, opposing to the fox hunting ban, both pro and anti Brexit, climate change...).