One of Tony Blair's former closest aides has been made chief of staff at Downing Street.
Mr Heywood moves from the Cabinet Office to Downing St
Jeremy Heywood, who was the former PM's principal private secretary from 1993 to 2003, will replace Tom Scholar.
It means he will be the senior civil servant at 10 Downing Street. He is moving from the Cabinet Office, where he was head of domestic policy.
Mr Scholar will move to the Treasury where he will take charge of moves to prevent another credit crunch crisis.
Mr Heywood, a career Treasury civil servant who once worked for Conservative Chancellors Norman Lamont and Ken Clarke, played a key role managing the sometimes fraught relations between Downing Street and the Treasury when he worked with Mr Blair.
The BBC's political editor Nick Robinson said the appointment was aimed at strengthening the organisation and decision making at Number 10, which has come in for criticism since Mr Brown took over as prime minister.
The appointment comes just weeks after Mr Brown brought in Stephen Carter - the chief executive of one of the City's best-known communications firms Brunswick Group LLP - as his chief of strategy, and personal adviser.
Mr Scholar is returning to the Treasury to be as managing director, International and Finance, in charge of domestic and global markets and institutions.
After working for Mr Blair, Mr Heywood, 46, joined Morgan Stanley as co-head of the UK investment banking division, before returning to the civil service in May last year.
Number 10 has not had a permanent secretary since Labour came to power.
Mr Blair is said to have tried to convince Sir Richard, now Lord, Wilson that the post should be created, but was turned down.