Merging the NIO with the Scottish and Welsh Offices would be "extremely foolish", the Conservatives have warned after it emerged that Shaun Woodward could be Northern Ireland's last Secretary of State.
Whitehall sources have revealed the Prime Minister Gordon Brown is actively considering the end of the NIO if he reshuffles his Cabinet next month.
A Department of the Regions — taking in the NIO and its counterparts in Edinburgh and Cardiff — has been a serious Government option since the devolved assemblies were set up.
But it has been repeatedly put off because of difficulties here.
Now sources say Mr Brown is considering a Cabinet promotion for Shaun Woodward and could merge the regional ministries at the same time.
But the Conservatives attacked the suggestion yesterday.
Spokesman David Fry said the move would "have more to do with Labour Party internal politics than any consideration of what is best for Northern Ireland".
"I've no doubt that Shaun Woodward is eager for promotion and would happily see the job of Secretary of State abolished, but we are equally sure that Northern Ireland needs to be properly represented around the Cabinet table," he said.
He said this was the wrong time "to even consider such a move".
"The Northern Ireland Executive has not met in ages and the political institutions are still weak, so to suggest abolishing the Cabinet position of Secretary of State for Northern Ireland is extremely foolish."
He said Shadow Secretary of State Owen Patterson had pointed out that "the institutions need further refinement and it is important that there is a senior Cabinet figure to oversee those developments.
"Mr Patterson has also maintained that, given the close links with the Irish Republic and the interest in Northern Ireland in the US, it is important that the position of Secretary of State for Northern Ireland is retained.
"Many would argue that Northern Ireland has suffered in the past from not being at the heart of UK politics and as a party we are determined to ensure that no longer happens."