On the conclusion of his term, Erskine returned to the United Kingdom and served as the Member of Parliament for Brighton from 1940 to 1941.

John Erskine married Lady Marjorie Hervey, the elder daughter of the 4th Marquess of Bristol, on 2 December 1919 and had four sons.

With an interest in politics and an allegiance to the Conservative Party, Erskine was appointed Assistant Private Secretary to Viscount Long in 1920.

William Joynson-Hicks, then a rapidly rising Conservative Minister, appointed Erskine as his Parliamentary Private Secretary in 1922, which gave him considerable interesting work to do.

This appointment effectively silenced Erskine in the Chamber of the House of Commons due to the tradition that Whips do not make speeches.

Previously Erskine had been an effective and confident speaker who had taken a close interest in the affairs of India (although he admitted never to having visited it).

Erskine decided to form an interim provisional Government with non-members and opposition members of the Legislative Assembly.

He first offered the Prime Minister post in the interim government to V. S. Srinivasa Sastri but Shastri refused to accept it.

Then Erskine formed the interim Government with Kurma Venkata Reddy Naidu of the Justice Party as premier on 1 April 1937.

On 22 June, Viceroy Linlithgow issued a statement expressing the British Government's desire to work with the Congress in implementing the 1935 Act.

[6] Erskine also opposed Rajagopalachari's usage of the Criminal Law Amendment Act of 1932 during the 1938 Anti-Hindi agitations:"..[Rajagopalachari] was too much of a Tory for me, for though I may want to go back twenty years, he wishes to go back two thousand and to run India as it was run in the time of King Ashoka".

On 21 February 1940, Erskine repealed the unpopular law imposing compulsory study of Hindi in the Madras Presidency.