This annotated Coxford Lecture is the first account dedicated to tracing the part played in the 1980-82 patriation of the Canadian Constitution by the British House of Commons, particularly by its Select Committee on Foreign Affairs. This committee, for which author was the adviser, investigated the propriety of the UK Parliament’s acceding to a request for amendment of the British North America Act 1867 (as amended) if the amendment were opposed by a substantial number of Provinces and it would affect their powers. Against the firm opposition of the Canadian government (secretly being assisted by the British government), the Committee reported in January 1981 that acceding to such a request in such circumstances would be a breach of Parliament’s constitutional responsibilities. A second report, in April 1981, defended that opinion against the Canadian government’s vigorous attempt in March to refute it. The Committee’s position strongly resembles that of the “conventions” majority of the Canadian Supreme Court in September 1981. But the resemblance should not obscure a significant difference, rooted in the distinct authority of the UK Parliament during this terminal phase of the patrimony that, by Canadian decision in 1931, it had inherited: some imperial responsibilities (by then only procedural, and terminated in 1982) for the polity and people of Canada.