That was not Reform. It was Tommy Robinson, someone so politically toxic that Reform turned down a huge amount of money (a £80m donation) from Elon Musk because it came with the condition that they allowed him to join the party.

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...).