This section is divided by diarist:
- UKC/JOH/DIA/D1 : Hewlett's diaries
- UKC/JOH/DIA/D2 : Mary Johnson's diaries
- UKC/JOH/DIA/D3 : Nowell Johnson's diaries
- UKC/JOH/DIA/D4 : one diary kept by Hewlett's father, and one by his sister-in-law, Alice
These are a mixture of appointment, personal and travel diaries. The longest continous set of Hewlett's diaries run from 1930-1965 and Mary's from 1937-1929. Nowell's diraries do not form such an uninterrupted 'set', but focus on the late 1950s and early 1960s.