The name of Arnold Leese was never as famous as that of Oswald Mosley, nor was the former's Imperial Fascist League ever as popular as the latter's British Union of Fascists.
Leese had been a veterinarian working in India and East Africa before returning to England having served in the Great War. As an animal lover, his hatred for the Jews grew out of his disgust at the animal cruelty in the Levitical dietary laws. He had been a member of the British Fascisti before founding the IFL at the end of the 1920s; when Mosley formed his own party, a merger was proposed but rejected on account of what Leese saw as deficiencies in Mosley's fascism. Leese found the BUF to be sorely lacking in the sort of full-bore biological anti-semitism and racial ideology that his own group and the National Socialists of Germany had been contemporaneously promoting: he even referred to the BUF as the "British Jewnion of Fascists". In reaction to this refusal and opposition, the Blackshirts attacked and closed down IFL meetings, effectively shutting down their competition. Reading through
an October 1934 issue of the IFL's party organ, I was amused to see the writer takes offence at a throwaway remark of Mussolini's, implying the inferiority of the Nordic in comparison to the Mediterranean. He criticises Il Duce and moves the racial goal posts so that both peoples can be classified as one indivisible Aryan race. This is a classic example of a problem that will be encountered by any sort of supremacist: there's always someone out there more bigoted than you.
Leese is sometimes credited with being the first person, from as early as 1928, to have advocated gassing the Jews, but this is false: Kaiser Wilhelm II had, in a letter to Field Marshal von Mackensen, recommended the same solution just under a decade earlier.