On the eve of the Suez Crisis, he was present at the crucial meeting on 25 September 1956 where Harold Macmillan was apparently persuaded that US President Dwight D. Eisenhower had offered the British Government tacit support; Makins, on the other hand, correctly concluded that Eisenhower would not support the intervention.

[4] After his return from Washington he served as Joint Permanent Secretary to The Treasury from 1956 to 1960 and as Chairman of the United Kingdom Atomic Energy Authority from 1960 to 1964.

The couple had six children:[6] Makins was appointed to the Order of St Michael and St George as a Companion (CMG) in the 1944 New Year Honours[10] and was promoted in the same Order as a Knight Commander (KCMG) in the 1949 Birthday Honours.

[12] He was promoted in the Order of St Michael and St George as a Knight Grand Cross (GCMG) in the 1955 New Year Honours[13] and was promoted within the Order of the Bath as a Knight Grand Cross (GCB) in the 1960 New Year Honours.

[14] In the 1964 Birthday Honours, Makins was raised to the peerage as Baron Sherfield, of Sherfield-on-Loddon in the County of Southampton.