The 'horseshoe cabinet' where Mandelson is at PM's right hand

Shaun Woodward, the Northern Ireland Secretary and a former Tory MP, has won a place in Gordon Brown's inner circle and a seat at the horseshoe-shaped table in the Prime Minister's Downing Street "war room".

Mr Woodward is a close ally of Lord Mandelson, who has also landed a berth in the "kitchen cabinet" for the first time, perched at Mr Brown's right hand – symbolising his role as the Prime Minister's consigliere. The Business Secretary was appointed First Secretary in the Cabinet reshuffle – Deputy Prime Minister in all but name.

The moves are part of a wider shake-up aimed at improving the Downing Street machine as the Prime Minister tries to fight back after surviving a coup attempt. Simon Lewis, a public relations consultant with wide experience in business, and who advised Buckingham Palace following the death of Princess Diana, is to become the new head of communications at No 10.

Lord Mandelson and Mr Woodward are the two newcomers to Mr Brown's top table. They replace Liam Byrne, who moved from the Cabinet Office to become Chief Treasury Secretary, and Tom Watson, a Brown ally who stood down as a Cabinet Office minister.

Mr Woodward is an unlikely ally for Mr Brown. He has recently sat next to him during Commons statements, whispering advice, as he did on Monday when the Prime Minister announced an independent inquiry into the Iraq war. It is a role that Lord Mandelson cannot perform because he is not an MP.

Mr Woodward, the Cabinet's richest man, is married to the supermarket heiress Camilla Sainsbury. He was viewed with suspicion by some Labour MPs after crossing the Commons, but is seen in No 10 as a source of intelligence on David Cameron's thinking and likely strategy. Mr Cameron worked at Tory headquarters at the 1992 general election, when Mr Woodward was the party's director of communications, and later took over Mr Woodward's former seat in Witney, Oxfordshire.

The war room is based in 12 Downing Street and linked to No 10 via a corridor running through No 11, the base of the Chancellor Alistair Darling. The L-shaped room in No 12 was occupied by government whips, but was commandeered for the PM's press office when Alastair Campbell was Tony Blair's communications and strategy chief.

Also in Mr Brown's war room, but sitting away from the main table, are Sue Nye, his gatekeeper and now Downing Street's head of external relations; David Muir, the head of political strategy recruited by Lord (Stephen) Carter, the former strategy chief; and Nick Pearce, who heads the No 10 policy unit.

In a side-room, so they can have the live TV news channels blaring, is Mike Ellam, the Prime Minister's press secretary and director of communications. He will return to the Treasury next month and be succeeded by Mr Lewis. Housed in the same room are Justin Forsyth, head of strategic communications, and two party political spin doctors, Michael Dugher and John Woodcock. The latter is expected to move to a new Downing Street role to boost coherence of Labour's message in the run-up to the general election.

Key staff used to complain that it took too long to find each other during a crisis when some were hidden in the "rabbit warren" of No 10. Mr Brown set up the war room last year after Michael Bloomberg, the Mayor of New York, gave him a tour of his office, which is run on similar lines.

When the Prime Minister is not sitting at his desk at the bottom of the horseshoe, he works on speeches or makes calls from a side office in No 12. He switches back to No 10 to receive visitors, normally in the Thatcher Room, and to chair meetings of ministers.

The war room was where Brown loyalists were scrambled to at 10pm two weeks ago after James Purnell resigned from the Cabinet and provoked a leadership crisis. "It was a fitting place. We were in a war," said one member of Team Brown.