"A field cornet is a term formerly used in South Africa for either a local government official or a military officer. [...] As such, a field cornet performed important functions in administrative, judicial and police matters. In addition, in peacetime the field cornet was the head of the militia, was responsible for maintaining law and order in his area, and was tasked with supervising the handover of postal items on arrival in his district." [Source: Wikipedia]
As the only authority permitted to appoint further field cornets, it was Lombard that certified Leake in this capacity.