Sorry if this is extremely generic. I've been looking for anything involving some sort of secret police or internal investigation force in 18th-19th century Great Britain. I assume due to poor wordage on my part I haven't been able to find anything of the sort before the 20th century.

I'm writing a story of a parallel world where I plan to have my character's properties investigated by the governing state (if it were possible). This state is a reflection of Great Britain basically at the height of her empire; however, the world as a whole functions coherently based on the 18th and 19th centuries.

The character is an advisor in one of the nation's many parties that are elected to their parliament, he is not a seated member. He's the lord of a large and mostly isolated estate in the country side where he handles his duties as an international agent for a secret, ancient organization; perhaps maybe not almost kinda sort of like the 'illuminati' but 100% real and wilder. Character accidentally gets caught up with his "unorthodox" duties in public at the nation's capital.

So if an antagonist wanted to indict my character, what could he do? How powerful would an antagonist have to be where he can credibly accuse him of treasonous or highly illegal acts?

If he did, is there a possibility that someone would or could order an investigation on my character's properties off the words of a sufficiently influential person?

Let's say by the king's decree, my character's properties will be investigated; estate, office, any building he's been known to work or frequently visit. If so, who would carry out the physical investigation; a police force, volunteer force, or even military forces?

If you have any links relating to the subject or that can help me better understand what I'm looking for, I would appreciate it!

I do not plan to have my story be a paradigm of historical fiction, but I do enjoy drawing from history when possible if I feel like it adds a fresh scent of realism.