Prime Minister Tony Blair said on Tuesday it would be hard for him to leave office but acknowledged it was the right thing to do.
Blair recalled his government's achievements in three terms in office in his last speech as leader to the annual conference of his governing Labour Party. He said the only legacy he cared about was Labour's winning a fourth term.
"The truth is, you can't go on forever," he said. "That's why it is right that this is my last conference as leader."
"Of course it is hard to let go. But it is also right to let go. For the country, and for you, the party."
Blair said fighting terrorism would be a tough challenge to the party in the years after he leaves office but said staying close to the United States was crucial.
"Yes, it's hard sometimes to be America's strongest ally," he said, adding that close involvement in the European Union could also be difficult.
"At the moment I know people only see the price of these alliances. Give them up and the cost in terms of power, weight and influence from Britain would be infinitely greater."
"Distance this country and you may find it's a long way back," he said.