[2] The professor of history at Brock University, John M. McEwen, considered the War Diary to be the most historically valuable of the three.

[9] In the published versions Riddell omitted much sensitive information and in February 1935 the original diaries were deposited in the British Museum "to be reserved from the Public use for fifty years".

[11] A survey of 100 books on this era of British history discovered that nine-tenths of them contained references to Riddell, with the majority quoting from his published works.

His perceptive diary led John Grigg to say he was "the nearest equivalent to a Boswell in Lloyd George's life".

[13] In the summer of 1917, during Lloyd George's first year as prime minister, Riddell assessed his personality: His energy, capacity for work, and power of recuperation are remarkable.

He has an extraordinary memory, imagination, and the art of getting at the root of a matter....He is not afraid of responsibility, and has no respect for tradition or convention.

He is full of humour and a born actor....He has an instinctive power of divining the thoughts and intentions of people with whom he is conversing.