Northern Ireland's fragile power-sharing administration could be thrown back into crisis by a 'yes' vote in this year's Scottish independence referendum, a former key adviser to Tony Blair has warned.
It came as DUP MP Ian Paisley jnr warned a vote for Scottish independence would drive a "wedge into the hearts and souls" of Northern Ireland and ensure further division.
A referendum on whether Scotland should be independent will take place on September 18.
According to the latest polls, less than a third of Scots want to leave the UK, with 61% saying they supported the Union.
Writing in the Financial Times Mr Powell said: "Scottish independence in 2014, if it happens, will legally change nothing in Ireland, but will politically change everything, change it utterly."
Mr Powell said a 'yes' vote was unlikely to persuade Northern Ireland people to vote to join Scotland in leaving the UK.
"Politically, however, a 'yes' vote would open up the constitutional question in Northern Ireland at a very delicate time," he added.
"The Good Friday agreement did not settle the question but was rather an agreement to disagree and, crucially, to share power."
Mr Powell said the violence surrounding parades and flags illustrated just how delicate the balance remains.
"Republicans will up the ante in the wake of a 'yes' vote and in the run-up to the anniversary of the Easter Rising by demanding an early referendum on a united Ireland on the same principle as the Scots," he added. Meanwhile, Mr Paisley jnr also spoke of the dire consequences for Northern Ireland if Scotland voted for independence.
Addressing Sir Gerald Howarth, who had been speaking against separation during a debate in the Commons, he said: "Do you agree with me that the unnerving and unsettling effect that a division in this wonderful Union would have is that it would get the tails up of Irish republicans in my part of the kingdom, and would drive another wedge into the hearts and souls of people in Ulster?"
Sir Gerald replied: "Of course you are absolutely right to make that analogy, and to point to the consequences to which the Scottish National Party does not wish to draw attention."
Jonathan Powell was Tony Blair's most trusted aide at several key crisis points in Northern Ireland.
The former Downing Street chief-of-staff regularly flew into the province to talk privately to the parties.
He wrote a book about his experiences, published almost two years ago, called Great Hatred, Little Room: Making Peace In Northern Ireland. In it he reported secret back-channel contacts between the DUP and Sinn Fein going back to 2004