Shaun Woodward could be Northern Ireland's last Secretary of State if Prime Minister Gordon Brown decides to shake up his Government next month.

Mr Woodward's increasing closeness to the Prime Minister has paved his way for a Cabinet promotion in the expected reshuffle.

Whitehall sources also say Mr Brown is prepared to do away with the Northern Ireland Office as a separate Government department.

The NIO would be swallowed by a new Department of the Regions, also encompassing the Scottish Office and the Welsh Office.

Mr Woodward has been tipped to take over as Defence Secretary — one of the plum Cabinet jobs. It is a proposed move that has caused dismay and resentment in some sections of the Labour Party, since Mr Woodward has been in their ranks for less than a decade. He defected from the Tories as an MP in 1999 and was given a safe Labour seat two years later.

And the current Defence Secretary, former NIO Minister Des Browne, is being weighed up for a return to Belfast as the head of the new department.

Mr Browne, the MP for Kilmarnock and Loudon, is currently double-jobbing as the Scottish Secretary.

Mr Woodward was given the NIO brief — his first Cabinet job — by Gordon Brown when he became Prime Minister last year.

He has reportedly become a close adviser to Mr Brown, especially concerning the Prime Minister's current difficulties, and has been a frequent visitor to Chequers.

Mr Woodward was an adviser to former Prime Minister John Major during the final years of the last Conservative Government and is thought to have an insight into the challenges of an administration struggling in the polls.

He is reported to have told Labour colleagues that “it is 1991, not 1996” — a reference to the atmosphere before Mr Major's comeback victory in the general election of 1992, as opposed to his Government's decline before the 1997 loss to Labour.

Whitehall insiders say Mr Woodward is also seen by the Prime Minister as an articulate spokesman for the Government.

The proposal to merge the Northern Ireland, Scottish and Welsh Offices has been around since power was first devolved to the regions, but has been usually held back because of Northern Ireland's political difficulties.

But with the NIO handling few reserved matters — and seeking to devolve its last major brief, justice and policing, in the near future — the PM is said to be considering completing the merger.