There has never been a better time for the UK to play a role in Europe, Tony Blair said in his first major speech on the EU since giving up the presidency.
A new EU budget was agreed during the UK presidency
A new generation of leaders shared the UK's vision of an "open Europe", he told an audience at Oxford University.
The prime minister said an alliance was needed among pro-Europeans and the "genuine, practical Euro-sceptics".
Shadow foreign secretary William Hague said Mr Blair was among leaders who followed the wrong Europe policies.
Mr Blair said he believed the pro-Europeans were "none-the-less worried about the direction of European integration", while the "genuine, practical Euro-sceptics" were worried about "Britain's disengagement from Europe".
Each often had similar worries and a similar agenda, even if they drew different conclusions about Britain's capacity to change, he said.
Speaking to an invited audience at Oxford, Mr Blair defended his record on the European Union, and insisted he is optimistic about the long term future of the EU.
Britain was now in a much better place in Europe, he said, with the new membership of eastern countries helping to form a new consensus about the future.
"Today, we have a shining opportunity to become part of a new consensus about the EU in the 21st century," he said.
Mr Blair believes a new consensus has formed around issues such as jobs, energy, security and immigration.
Farm subsidies row
The UK should become an "enthusiastic" participant in forthcoming EU debates, Mr Blair said in his speech.
The UK's six-month EU presidency, which ended on 1 January, saw a new framework budget agreed for 2007 to 2013.
The acceptance came after months of negotiations over farm subsidies, financial support for new members and the British rebate.
But 2005 also saw rows over the start of negotiations on Turkey joining the EU, and French and Dutch voters reject the proposed EU constitution in referendums.
Austria, which has taken over the presidency, is now trying to revive debate about the constitution.
Mr Blair said the aim of the UK's presidency had been "setting out a pathway for change".
Referring to the contentious budget deal negotiations at the end of Britain's presidency, Mr Blair said the "fevered frenzy in parts of the British media did not help".
The deal achieved means Britain pays "around the same as France and Italy" and avoided a "mad isolation" for the UK, he said.
Mr Blair said he was optimistic because the "prevailing wind" in Europe was fundamentally shifting.
He argued: "The irony is that, after the shock of enlargement, the crisis of the referendums, the opening of accession negotiations with Turkey and the agreement of the budget with a firm process of reform midway through the next financial term, after all these alarms and excursions there has never been a better time to be optimistic in Europe or enthusiastic about Britain's part in it.
"Europe has emerged from its darkened room. It has a new generation of leaders. The new consensus is forming.
"Yes, there is still a debate to be had, but the argument in favour of an open Europe is winning."
'No strategic vision'
For the Conservatives, Mr Hague gave the speech short shrift.
He said: "If a new generation of leaders is now beginning to think seriously about a new, more open Europe it is because the last generation of leaders, Tony Blair among them, have been following the wrong road for Europe.
"Mr Blair can leave office pleased, as we all are, with the achievement of EU enlargement, but his tragedy is that he never developed a strategic British vision for Europe or created a new model for Europe with which the British people could feel at ease."
UK Independence Party leader Roger Knapman said the "open Europe" vision might be shared by European elites but not by the British people generally.
He asked: "Why should the British public be optimistic about a political Union which costs every family in this country over £60 per week, yet remains democratically unaccountable and does not learn from its' mistakes?"