Theresa May will set out her plans for Brexit in more detail after Britain's EU ambassador quit his job.
A scathing resignation memo written by Sir Ivan Rogers, the British ambassador to the European Union, hit out at “ill-founded arguments and muddled thinking” among politicians backing Britain’s exit from the bloc.
In the speech expected later in January, Theresa May will reportedly say Britain will pull out of the single market if the EU does not offer concessions on freedom of movement.
Foreign Secretary Boris Johnson and Brexit Secretary David Davis will contribute to the announcement.
No 10 sources insisted the claims were speculation.
Following Sir Ivan's surprise resignation, Mrs May moved swiftly to calm tensions by appointing career diplomat Sir Tim Barrow within 36 hours.
No 10 described Sir Tim, a former ambassador to Russia, as a "seasoned and tough negotiator" who will help the Government make a success of Brexit.
Mr Johnson said Sir Tim was "just the man" to secure the best deal for the UK.
Mr Davis added: "His knowledge of Brussels means he will be able to hit the ground running at a vital time, and steer UKRep throughout the negotiation period.
But the appointment of another mandarin to the role sparked anger from some staunch Brexiters.
Labour welcomed the appointment but called for the Government to set out a clear timetable for its Brexit plans in the wake of the resignation.
The party's Brexit spokesman Sir Keir Starmer warned that Sir Ivan's resignation was likely to be a "significant loss" for Britain.
He said it had raised "a number of serious questions" about the Government's preparations for Brexit negotiations.
Mrs May has said she will trigger Article 50 of the EU treaties before the end of March.
