THERESA May has launched a stinging attack on Boris Johnson’s government over the ousting of a top civil servant.

The former prime minister hit out at Michael Gove in the Commons during a debate on the departure of Sir Mark Sedwill as both Cabinet Secretary and the UK's national security adviser.

He will be replaced as national security adviser by Johnson’s pro-Brexit Europe adviser David Frost – a political appointment rather than an impartial civil servant.

Addressing Gove in Parliament, May pointed out she had served on the National Security Council for nine years during her time as a Cabinet member and PM.

“During that time I listened to the expert, independent advice from national security advisers,” May said in a decidedly harsh tone.

She continued: “On Saturday, my right honourable friend 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?”

Cabinet Office Minister 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.”

Theresa May was visibly unimpressed by the answer.

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The former PM joins opposition politicians and former mandarins in condemning the political appointment to the national security council.

It comes amid reports that Sedwill had been undermined by Johnson’s top adviser Dominic Cummings.

Tory ministers have hinted that the other vacancy opened up by Sedwill’s departure, Cabinet Secretary, will also be filled by a Brexiteer.