A mutiny in Dartmoor Prison on 24 January 1932 led to the setting up of a commission of enquiry under du Parcq.

His report was considered satisfactory and he was rewarded with an appointment to the King's Bench Division as a judge, receiving the customary knighthood.

On 5 February 1946, he was appointed Lord of Appeal in Ordinary and was created a life peer with the title Baron du Parcq, of Grouville in the Island of Jersey.

The UK government relied on the Committee for information on the Channel Islands and in September 1940 his first appeal for funds on the BBC's 'The Week's Good Cause' programme raised what was then a record result.

du Parcq was also the author of a four-volume biography of David Lloyd George, published between 1911 and 1913, though for unknown reasons he avoided referring to it later in his life.