I was reading an article about the Cato Street Conspiracy and it mentioned Lord Sidmouth having a spy network that was almost as successful as Walsingham’s under Elizabeth I. I tried to do some basic research, but couldn’t really find much.
Lord Sidmouth ran the Home Office for a small period. There's a few names we know of during the time;
William J. Oliver, a informer and possible provocateur, personally recruited (or approved by) Lord Sidmouth in 1817. Rumored to be connected to the Pentrich Uprising.
John Castle, who had a role in the Spa Field Riots, was supposedly recruited by John Stafford in/around 1815 to infiltrate and provide false testimony regarding the Spenceans.
John Stafford himself, was a known spymaster for the Home Office, with dozens of known recruitments under his belt of varying sorts, some other names I could find; John Williamson, John Shegoe, James Hanley, George Edwards and Thomas Dwyer.
I wouldn't say so much that Lord Sidmouth had a spy network himself, rather having multiple spymasters under his employ.