The government’s top Brexit official, Oliver Robbins, has left the Department for Exiting the European Union and is moving to the Cabinet Office to work more directly for the prime minister.
It is understood there had been tension between him and Brexit Secretary David Davis, the BBC’s Laura Kuenssberg said.
She added that the move was also part of Theresa May taking more control of Brexit negotiations.
Mr Robbins will continue to lead the UK officials working on the talks.
The government said the appointment would “strengthen cross-government co-ordination of the next phase of negotiations with the European Union”.
It said Mr Robbins would continue to work closely with Mr Davis in his role as the leading “Sherpa” working on talks between UK and EU officials.
Philip Rycroft, currently second permanent secretary at the department, has been made permanent secretary.