I read this approx 5 years ago but I couldn't say if it was newly published back then; it was a hardback from a UK library.
I can't recall too much of the story, the only thing that sticks in my mind are these scene(s)...
There are two entities from a dark dimension, they are constrained by magical barriers and have been like that for decades.
They have adopted the personae of two English public school Prefects and spend all their time in a 'study' where they are always drinking tea and talking like 1950's schoolboys.
As I recall, there was a great fear of these two Prefects ever breaking the barriers and being loose upon the world. They were used as a source of information by the protagonists.
I want to say author Robert Rankin or Charles Stross, I have a few books by those gentlemen but sadly none with the story memories.