NOC - Non-Official Cover: British Secret Operations (Paperback) (ISBN-13: 9781732966109)

"WE WERE INSTITUTIONAL KILLERS in disruptive actions on the black, that is to say we made illegal entries across borders to perform dirty work, then returned home mostly without the knowledge or connection to the local British embassy's staff assigned to other covert affairs. The main job description was called deep cover within SIS, though the U.S.-led NATO preferred NOC or non-official cover - either description was undeclared. I served in various divisions in charge of different continents, often living like a mole..."

The first installment of The NOC Trilogy by Nicholas Anderson.