Reddit reviews In the Highest Degree Odious: Detention without Trial in Wartime Britain

The definitive and most comprehensive source is Simpson's masterpiece, 'In the Highest Degree Odious: Detention without Trial in Wartime Britain'

That is quite an expensive and long book, but it is comparatively objective and written by a legal historian who eventually became Professor of Law at Michigan Law School. That said, I think it is quite hard to look at the issue without having some element of victors bias, as the specific context that Churchill faced was chaotic and difficult.