Joined CRD in 1952 and specialised in Atomic Energy and Finance before becoming Head of Economic Section in Jan 1960. CRD Director Jan 1965-Oct 1970, working closely with Edward Heath and the Shadow Cabinet. During this time Sewill was also Secretary to the Advisory Committee on Policy. He was Special Assistant to the Chancellor of the Exchequer (Anthony Barber) Oct 1970-Mar 1974, and Adviser on Public Affairs to the Committee of London and Scottish Bankers (now the British Bankers' Association) 1975-1990.