After peace was declared in June 1902, he left Cape Town to arrive in the United Kingdom the following month.

[5] Clarke served in the First World War, being made an assistant quartermaster general in December 1914[6] and then briefly commanding the 23rd Infantry Brigade from July to September 1915.

[8] In this role he was responsible for transferring Allied prisoners of war back to the United Kingdom and he strove to ensure they were treated properly and given clothing and blankets as they returned from Germany.

[10] After the war Clarke was promoted to the permanent rank of lieutenant general in June 1919[11] and became Quartermaster-General to the Forces; he retired in 1926.

The couple had one son, John Walrond Edward Clarke (1913–1987) of Clough, County Down, before Mary's death in the outbreak of Spanish flu in 1918.