The Lisbon Treaty, signed by EU leaders in Portugal’s capital in December 2007, resurrected most elements of the controversial European Constitution thrown out by French and Dutch voters four years ago.
It also survived a referendum rejection in Ireland last year when the Irish reversed their first decision in a second vote held in October.
The Labour government broke a 2005 general election promise to hold a referendum and last month the Conservatives withdrew a pledge for popular vote, effectively ending British debate on Lisbon Treaty.
Senior officials are relieved that a long period of political uncertainty surrounding the Lisbon Treaty is finally over.
“I’m delighted that we now have the right institutions to act and a period of stability, so that we can focus all our energy on delivering,” said José Manuel Barroso, president of the European Commission.
The Lisbon Treaty created a new EU President and foreign minister.
Appointees to the posts, Herman Van Rompuy and Baroness Ashton, joined other senior Brussels officials, for celebrations in Lisbon on Tuesday night.
EU officials are delighted with the treaty which has increased powers for the Commission, MEPs and the European Court of Justice.
Dozens of national vetoes, especially in the area of justice and home affairs, have been scrapped in order to “streamline” EU decision-making.
Jerzy Buzek, president of the European Parliament, marked the day by sending flowers to be placed on the graves of Jean Monnet and Robert Schuman, the “founding fathers of the EU”.
“This marks the beginning of a new era of European integration,” he said.
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