While you're waiting for a fuller answer, you might find an older post of mine useful (drawing in turn on this answer), discussing the extent that anti-fascist activism should be credited with preventing fascism in Britain. As I concluded there, anti-fascism is at best one piece of the puzzle, with the failure of British fascism (and extremist politics more generally) ultimately best explained by the durability of mainstream politics and institutions in Britain. Hopefully someone else is able to discuss this in more depth.

You might also want to check out this post by u/Vespertine, discussing the basis of the British Union of Fascists' appeal and the extent they actually had a strong following.

Post-war Germany was a complete mess under the Weimar government with the Spartacist revolt, Kapp Putsch, hyperinflation, financial crash etc whereas post-war Britain wasn't nearly as chaotic, meaning extremist politics didn't rise to the forefront to the same extent they did in Germany and other European countries.