Theresa May has criticised the PM’s appointment of his Brexit negotiator to be his new national security adviser.
Speaking in the Commons, she suggested David Frost did not have the required expertise or independence to succeed Sir Mark Sedwill in the role.
Labour said the choice of Mr Frost, who is currently leading the UK’s trade talks with the EU, was “dangerous”.
But Cabinet Office minister Michael Gove said Mr Frost was highly qualified and would be accountable to the PM.
Mr Frost is a former civil servant, having left the Foreign Office in 2013 to work in the private sector.
He is due to take on the role at the end of August, at which point Sir Mark will also stand down from his other role as cabinet secretary, the UK’s top civil servant.
Mrs May, who appointed Sir Mark Sedwill to both roles when she was PM, told MPs that during her nine years as a member of the National Security Council, she had “listened to the expert, independent advice from national security advisers”.
She asked Mr Gove how Mr Frost’s appointment squared with remarks he made in a recent speech on civil service reform on the need to “promote people with proven expertise”.
“Why is the new national security adviser a political appointee with no proven expertise in national security?”
‘Needs of the hour’
Mr Gove said there were precedents for non civil servants to take on key roles serving the PM and that the official that oversees senior government appointments agreed this was appropriate in this case.
He said Mr Frost would neither be a civil servant nor a special adviser but would have the status of an envoy.
“We have had excellent national security advisers in the past, not all of whom were steeped in the national security world but were distinguished diplomats in their own right,” he said.
“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.”
But Mrs May was seen to shake her head vigorously while Mr Gove was speaking.
The two have clashed in the past, most notably over extremism in schools, when they were members of David Cameron’s cabinet. Mrs May sacked Mr Gove when she became PM in 2016 but subsequently brought him back.
The role of national security adviser was created by David Cameron in 2010. Its previous occupants, Sir Peter Ricketts, Sir Kim Darroch and Sir Mark Lyall Grant, were all senior career diplomats.
Former Foreign Secretary Lord Hague has added his voice to those concerned at Mr Frost’s appointment, saying it had “raised eyebrows” and possibly “sharpened daggers” within the defence and intelligence communities.
In his weekly column for the Daily Telegraph, the former Tory leader said that while the ex-diplomat was “highly capable”, the role was better suited to someone with first-hand experience of security operations.
Warning about the danger of US-style politicisation of senior government roles, he added: “If we want the most promising people to serve the country, they have to come from varied points of view.
“All of us who have dealt with US administrations have witnessed the nightmare of changing long lists of officials when a new President comes in, leading to extended vacancies, loss of expertise and serious damage to diplomacy.”