In 1934 he was posted to the Royal Bombay Sappers and Miners at Kirkee as a company commander in the training battalion. He returned to Britain in 1936 and joined the Twenty-third Field Company at Aldershot. Moving to the First Field Squadron, he stayed at Aldershot while the unit was being mechanised. While at Aldershot, Jefferis successfully raced horses and played squash competitively. He was promoted major on 6 June 1938, and on 4 April 1939 he was appointed a General Staff Officer, Grade 2.