Stirrup, a Air chief marshal who is the nation's most senior military officer, is to resign this fall before the end of his term, The Sunday Times of London reported. He and Jeffrey were both seen as closely tied to Labor, which recently relinquished power to a Conservative-led coalition led by new Prime Minister David Cameron.
The changes are seen as a sign of the new government's dissatisfaction with the results obtained in Afghanistan and budget issues, The Sunday Times said.
Fox told the newspaper he would put "the best people" in the posts following a strategic defense review to be completed this fall.
"We have to be able to maintain full stability and the full confidence of the people who work for us, not least because we're in a very dangerous armed conflict," he said.