John Steed's - Irregulars
While Steed mainly works with his partners, he occasionally recruits irregulars during his investigations when he needs information about a person or if he wants to keep someone under surveillance.
These sources are just ordinary people, but quite necessary for his work, because nobody seems to take any notice of them but they see and hear anything. While his partners are not on the payroll of the Ministry, Steed pays the irregulars for their service, and they follow his orders in return.

The Frighteners, series 1

The flower seller at King's Road whispers something in his ears, and he pays the waiter of the Italian restaurant for some information.
Steed gives Grekio, a man in a bus conductor uniform, some orders.
"Tell Walters to be there in the morning when our young gentleman leaves his flat"
"All right, you can stand down."
And who would ever suspect that two charming old ladies who also work for John Steed in series 3 episode November Five? But they secretly hand over a note to him and follow Major Swineburn on Steed's order.