He has been described as one of the greatest English civil servants of his time, and is credited with building up an intelligence service as efficient as that which John Thurloe had operated under Oliver Cromwell. His detailed notes of Privy Council meetings are an invaluable source of information about its operation, especially in the political crisis of 1678–79. On the other hand, he was a poor public speaker: even Charles II, himself a very hesitant speaker, complained of his "droning".