Very good at presenting the competing ideological views and also avoids the trap of poor AH that if X doesn't happen [Labour victory in 1945, Rise of Nazis in 1933, Election of Thatcher in 1979] the pre-X polity and economy will be preserved in aspic. It doesn't happen that way, the other side have aspirations and programmes of their own and the economy will change in response to technological, demographic and climatic changes whatever the politicians do.
OTL Noel Pemberton-Billing was Britain's Joseph McCarthy but definitely a case of "Great wits are near to Madness very close allied. And what thin partitions Sense from Thought divide". Unlike McCarthy, Pemberton-Billing could have been a distinguished, even a great man if he hadn't been pathologically anti-Semitic and homophobic.
The man was intellectually extremely capable (learned Latin over a weekend in order to take a law degree), founded Supermarine and designed Britain's first seaplane (plus some cameras and recording equipment). He also came off with a lot of very unpleasant accusations of sexual corruption in high places controlled by German Intelligence that were frankly barking. Though even there he is bright, if mad, "Germany has found that diseased women cause more casualties than bullets. Controlled by their Jew-agents, Germany maintains in Britain a self-supporting – even profit-making – army of prostitutes which put more men out of action than does their army of soldiers." Very nasty, but at the same time he picks up one of the most salient points about warfare that few civilians ever realise -that incapacitating your enemy is preferable to killing him as that way he remains an ongoing drain on resources. So nasty but bright with it.
Is the POD here that he didn't go obviously off his rocker and stayed comparatively sane?
He isn't involved in the POD but the Britain that emerges from the POD is more conducive to men like Pemberton Billing than OTL.