The post war memoranda kept the standard notation with a change of internal reference; CP (45)315 refers to the 315th paper put before the Cabinet in 1945. Similar to post-war conclusions, the internal references were changed periodically. Care must be taken in years where there are two different internal references in use to ensure the correct meeting is identified; for example, there are two (51)1 papers, one under the CP reference (for the Labour government under Attlee) and one for the C reference (for the Conservative government under Churchill which took power later in 1951).
CP is used 1945-1951, 1955-1957, 1963-1964, 1970-1974, 1976-1979
C is used 1951-1955, 1957-1963, 1964-1970, 1974-1976