The British government considered redrawing the border of Northern Ireland, and transferring more than 500,000 people, in an effort to defeat terrorism in 1974.
Documents released today under the 30-year rule show that Harold Wilson ordered that the option should be considered, in the wake of the collapse of power-sharing, and continuing IRA violence.
1974 began on a note of optimism in the North, as the first power-sharing executive took office following the Sunningdale Agreement.
But five months later, in the face of a loyalist strike, the executive collapsed.
According to the secret documents made public today, Mr Wilson accepted that a repeat of the strike would leave his government at the mercy of the loyalists, as the Army was virtually powerless to maintain essential services.
As a result, the British government considered a 'Doomsday scenario' where the border would have to be redrawn.
Officials advised Mr Wilson that this would mean the forced transfer of up to 400,000 Catholics and 150,000 Protestants.
Despite this the British Prime Minister ordered further consideration of repartition - including the possibility of making independent that part of the North which was not incorporated into the South.