The Northern Ireland Secretary, Mr Peter Mandelson, assured unionists last night that only the Union flag would be allowed to fly over government buildings in Northern Ireland.
Opening the debate in the House of Commons on the Flags (Northern Ireland) Order 2000, Mr Mandelson urged politicians not to allow clashes over symbols to become a permanent source of division in the future.
The order, allowing Mr Mandelson to intervene if the Executive and the Assembly cannot agree on flying the Union flag on public buildings, was approved by 240 votes to eight.
"I believe myself that this difficult, though symbolic, issue would be best resolved by the executive committee itself," Mr Mandelson said. "I believe practice in Northern Ireland should reflect practice elsewhere in the United Kingdom."
Mr Mandelson said the Good Friday agreement enshrined respect for the identities, ethos and the traditions of all in the community and they should not be forced to accept and to fly the flag of somebody else's tradition.
"The Union flag remains the flag of the UK of which Northern Ireland is a constituent part and while that is the wish of the majority of its people it will continue, therefore, to fly over Northern Ireland," he said.
Mr Mandelson stressed: "I don't want to see the Executive consumed for weeks and months by shadow boxing over an essentially symbolic issue.
He said he would only exercise the reserve power in consultation with the Northern Ireland Executive and Assembly.
Ulster Unionist Party leader, Mr David Trimble, warned the order could be laying the foundations for future divisions.
He said it was necessary the legislation go through and go through quickly so the issue could be settled.
"Unfortunately, however, I think that the form of this order is not going to settle the issue and I think there may be seeds for future trouble," he said. Putting the flying of the Union flag on a legal basis would not have been necessary if nationalists had followed the Belfast Agreement because it had recognised the legitimacy of Northern Ireland within Britain, he said.
"The issue should not have arisen but it has arisen because some nationalists don't actually in practice operate the agreement and are failing to implement it," Mr Trimble said.
He described assertions made by the Minister for Foreign Affairs, Mr Cowen, that institutions in the North should have no element of Britishness as "utterly unacceptable, quite wrong and completely contrary to the agreement".