One of Britain’s most powerful tools against external and internal threats was the Secret Department of the Post Office and its Deciphering Branch. Established in the second half of the seventeenth century, the Secret Department was located within the warren of buildings that comprised the headquarters of the General Post Office on Lombard Street at the centre of the City of London. It was financed off-the-books from secret service monies controlled by the Secretaries of State and omitted from the Post Office’s accounts. The agency was expanded during the first half of the eighteenth century in line with the demand for its output to the extent that by the late 1730s the interception, opening, copying, and decryption of correspondence was undertaken on an almost industrial scale.

Although occupied mainly with London’s postal service and mail routed through the capital, the department also sourced mail intercepts via a network of agents across Britain and Ireland, with additional material gathered through agents overseas. Among the many sources were port officials reporting on ship movements and troop deployments, bribed post office officials across continental Europe, and a network of intelligence agents.

The Secret Department was run by Jean Le Fevre (anglicised as ‘John Lefebure’) (d.1752), who had joined the Post Office as a clerk in 1715. Three years later he was promoted to head the Department, which included decoders and decipherers. Lefebure’s nominal position appears in Chamberlayne’s Magnae Britaniae Notia and Miège’s The Present State of Great Britain, which give his title as Foreign Secretary and record his salary as £50 per annum. But the designation of a low level clerical role and the pay grade which would substantiate such a pedestrian position were false and designed to understate his importance. Evidence to the Committee of Secrecy published in 1742 records that Lefebure, who reported through Delafaye, earned around £800 per year, sixteen times higher than the published figure. It placed Lefebure at almost the same pay grade as Delafaye and well within the upper decile of London Society.

Like Delafaye, Lefebure was a Huguenot and a freemason. He is recorded as ‘Le Favre’ in the membership list of the King’s Head lodge in Pall Mall; other members of the lodge also acted as British spies. As an émigré whose family had found sanctuary in England, he was loyal to the Crown, unstinting in outing potential Jacobite threats, and proactive in requesting warrants to detain and open suspect letters. Indeed, it was on Lefebure’s watch that the 1717, 1719, and 1721 plots were uncovered.

The Secret Department was relatively small in number but it’s Huguenot and Masonic connections were large. Aside from Lefebure, its employees included Peter Thouvois and Peter Hemet, the latter a member of Martin Folkes’s lodge at the Bedford Head in Covent Garden. And alongside them was Anthony Corbière, a senior decipherer. Delafaye’s colleagues included other Huguenots: John Couraud, the senior clerk at the Southern Department and later Delafaye’s replacement in the pivotal position of Secretary to the Lords Justices; John Larpent, chief clerk at the Northern Department; and Daniel Prevereau, clerk and later chief clerk under Delafaye at the Southern Department.