Commissions High is an account of the work of the Canadian High Commission from 1870 until Britain's entry into the European Common Market one hundred years later. Roy MacLaren argues that, until the defeat of Diefenbaker in 1963, there was tension between the forces of imperial (later Commonwealth) solidarity and those of localized nationalism. Commissions High explores how localized nationalism led Canadian politicians to resist British efforts to centralize imperial decision-making and shows how the weakening of Commonwealth and transatlantic bonds following World War II contributed to Britain's focus on Europe and to the increasing domination of Canada by the United States.

MacLaren, a former diplomat posted to London, offers an insider's perspective on immigration, Canada's trade and finance, the coronation of George VI, the Paris Peace Conference of 1919, and NATO. For many years the position of high commissioner was so important that the incumbent had to be a minister in the Canadian government. MacLaren argues that, despite today's shift in Anglo-Canadian relations, a political appointee can be more effective in the role.