Former prime minister Theresa May has questioned why her replacement Boris Johnson has chosen a "political appointee with no proven expertise" to be the government's new national security adviser (NSA).
Backbencher Ms May attacked Prime Minister Johnson's recent decision to appoint one of his closest allies, David Frost, to the National Security Council, suggesting he would be unable to provide "expert independent advice".
Sir Mark Sedwill - the person being replaced by Mr Frost - was appointed Cabinet Secretary and NSA by Mrs May during her time in office but it appears the influence of Dominic Cummings in the current government may have spelled the end for the UK's former top civil servant.
Sir Mark announced over the weekend he will step down in September and the UK’s current Brexit negotiator Mr Frost is set to take up the role.
ITV News Political Editor Robert Peston said Mr Frost "is close to Dominic Cummings" and his appointment is being viewed as a win for the prime minister's top adviser.
In his new role, Mr Frost will continue as a political adviser rather than becoming a member of the civil service and a formal process will begin to find a new cabinet secretary to replace Sir Mark.
The prime minister has faced criticism for appointing a political special adviser to a position previously filled by permanent civil servants.
Minister for the Cabinet Office Michael Gove said that it is “entirely appropriate” for the prime minister to choose an adviser “appropriate to the needs of the hour”.
During a Commons debate about Mr Frost's appointment, Ms May said: “I served on the National Security Council for nine years – six years as home secretary and three as prime minister.
"During that time, I listened to the expert independent advice from national security advisers.
“On Saturday (Mr Gove) said, ‘we must be able to promote those with proven expertise’.
"Why then is the new national security adviser a political appointee with no proven expertise in national security?”
Mr Gove responded: “We have had previous national security advisers, all of them excellent, not all of them necessarily people who were steeped in the security world, some of whom were distinguished diplomats in their own right.
“David Frost is a distinguished diplomat in his own right and it is entirely appropriate that the prime minister of the day should choose an adviser appropriate to the needs of the hour.”
Number 10 has also defended the adviser's appointment, saying such political appointments were not unusual in other countries.
“The appointment of the NSA is always a decision for the Prime Minister,” the spokesperson said.
“It is not unusual in other countries for ambassadors to serve as national security advisers and ambassadors can be political appointees. David Frost has the status of an ambassador.
“The First Civil Service Commissioner has agreed the appointment. That is consistent with the Constitutional Reform and Governance Act.”