IDK if he quite "spoke out" but he mentions them unfavourably in a few essays, sometimes indirectly. The one that comes to mind is "notes on nationalism" which

IDK if he quite "spoke out" but he mentions them unfavourably in a few essays, sometimes indirectly. The one that comes to mind is "notes on nationalism" which IIRCC has it listed along with republicanism, zionism & pacifism as examples of obsessive nationalism existing in the contemporary British left of his day. Hi did fight with a Trotskyist militia which included many republican volunteers from that era. That's why I mentioned them... and also the esperantists. They were his circle, I believe.