Black was chairman of Beaumont Properties Ltd from 1933 to 1980; chairman of the Temperance Permanent Building Society from 1939 to 1973; chairman of M. F. North Ltd 1948 to 1981; chairman of the London Shop Property Trust Ltd from 1951 to 1979; and the director of a large number of other companies. His private commercial interests were so extensive – he held 49 directorships – that an unsuccessful attempt was made to ban him from membership of the House of Commons.