From 1948-52, as British Ambassador in Washington, he greatly strengthened the relationship between the two countries. He negotiated the Atlantic pact (later the north Atlantic treaty and then the North Atlantic Treaty Organization, NATO), signed in April 1949. Post Washington he became chair of Lloyds Bank, the largest of the London clearing houses (1954-62) and then re-entered academic life.
From the mid 1950s he was often called upon by the government of the day to chair or play a major part in important public inquiries: administrative tribunals and inquiries (1955-57); the working of the monetary system (1957-59); on the development of India and Pakistan (1960); British business schools (1963); Oxford University (1964-66); section 2 of the Official Secrets Act of 1911 (1971-72); the Committee of London Clearing Bankers (1974); a register of immigrants' dependants (1976); and the British Government's conduct of the Falklands War (1982-83).
He was appointed a CBE (1942), a KCB (1946), and a GCMG (1952). He was made a life peer (1962) as Baron Franks, of Headington in the County of Oxford and received the Order of Merit in 1977.