Another perfectly adequate British writer from the stable of perfectly adequate British writers writing in m/m at the moment. Lots of genuinely lovely prose about the British countryside, nice bits of historical background about British artifacts/instituitions, a solid but ultimately bland romance, a decent stab at introducing an element of intrigue into what's really a middle-level, forgettable story -- it's all fine, just not expecially memorable.
The attempt to make one of the characters a super-spy either needed to be extended a whole lot, or collapsed altogether and used for laughs. As it was, I don't really associate insurance investigators with, you know, Bond. But points for trying to give the thing some plot.
You could do worse. The way m/m is atm, you could do a lot worse.