Britain's new Prime Minister Gordon Brown Thursday started his first full day in office with the appointment of David Miliband as the new Foreign Secretary, and a radical overhaul of the future shape of the British government.

David Miliband, the 41-year-old rising star of Britain's ruling Labour Party, was once closely associated with ex-leader Tony Blair.

He will be the youngest Foreign Secretary since the late 1970's in Britain and will replace Margaret Beckett, who served for just a year under Blair following the sacking of Jack Straw in May 2006.

Straw is tipped to return to the cabinet as head of the newly created Justice Ministry.

Among other high-profile casualties of the Brown renewal are Patricia Hewitt, who resigned as Health Secretary, and John Reid, the Home Secretary and leading "Blairite."

The appointment of Miliband, a former environment secretary, is intriguing as he had been pushed by the Blair camp to stand against Brown in the recent leadership contest.

But Miliband, always seen as a Blair supporter and potential future leader, rejected the challenge and publicly vowed his support for Brown. In the end, Brown had no challenger to the post of Labour Party leader.

His brother, Ed Miliband, has been a key adviser for Brown in the Treasury for many years.