NO10 is facing criticism after it was announced key Brexit negotiator David Frost will become the UK’s top civil servant.
It comes after Sir Mark Sedwill announced his resignation on Sunday after reported clashes with Dominic Cummings.
Mr Frost is currently leading talks with Brussels – but officials say the new appointment won’t affect his existing role.
There has been criticism that, unlike previous holders of the post, Mr Frost is a political adviser rather than a career civil servant, and lacks security experience.
Elsewhere, Boris Johnson has reportedly given the EU until September to confirm a trade deal.
Face-to-face talks on a deal between the EU and the UK have now begun in Brussels, after both sides pledged to “intensify” discussions.
This is the first time the Mr Frost and his EU counterpart Michel Barnier, have met face-to-face since talks started in March.
Negotiations took place virtually during the coronavirus pandemic.
Boris Johnson has said a deal could even be reached this month with “new momentum”.
He spoke with EU Commission President Ursula von der Leyen earlier this month.
This latest round of talks will continue all week, with Mr Frost and Mr Barnier expected to meet this Friday.
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