Jack Straw has sought to take the heat out of the simmering row over plans to shake up the European Union.
Straw and Blair will attend summit this week
The foreign secretary, speaking ahead of an EU summit where the proposed EU constitution will be discussed, said key decisions on the plans were some way down the line.
Mr Straw insisted the proposals were "an opportunity not a threat", saying they were only seen as a "menace" in "the parallel universe of extreme eurosceptics".
But the Conservatives have upped the pressure over the EU plans, setting the government 17 tests they say must be passed during negotiations on the plans.
This week's summit of EU leaders in Greece comes amid continuing calls for a referendum on the EU constitution, with the Tories saying those demands will only go away if their tests are met.
During prime ministers questions Tony Blair accused the Conservative of wanting the UK to pull out of the EU.
Mr Straw - casting the government as "confident Europeans" pursuing a course of "positive patriotism" - told a news conference that leaders at the summit outside Thessaloniki this week would decide when to begin an inter-governmental conference to thrash out a final treaty based on the draft EU constitution.
He said the IGC was likely to start in the autumn and end next year, stressing that each EU state would have a veto over every decision made.
The draft constitution is the result of more than a year's work by the convention on Europe's future.
It sets out a vision of the EU once 10 new states have joined, including proposals for a powerful EU president, foreign minister and a legally-binding charter of rights.
The plans have sparked calls for a referendum in the UK, with the Tories arguing they represent fundamental constitutional changes for Britain.
But Mr Straw argued that referendums are reserved for major constitutional changes - such as membership of the EC in 1975 or a future poll on joining the euro.
"Our default setting is that it is for elected parliaments to make decisions," he said.
And he said the draft EU constitution does not pave the way for significant constitutional changes.
The foreign secretary said that while British influence on the plans had been significant, many in the UK are "engulfed by self doubt" when it comes to Europe.
But he said: "There is no need for the self doubt which runs through so much of the euroscetic case.
"We are confident Europeans pursuing our national interests for a strong relationship with our European partners."
Mr Straw said the constitution represented a chance "to ensure that British interests in an expanded EU of 25 maintain the right balance between the union and the nation state and that the union becomes more effective on behalf of our citizens and more transparent".
Earlier, the Tories set Mr Blair 17 tests which they say must be met during negotiations on the convention in order to quell calls for a referendum.
Shadow Foreign Secretary Michael Ancram said the establishment of an EU constitution over-riding national constitutions must be "excised from the work".
He said the EU should not be granted "a single legal personality", while plans for a permananent EU president and foreign minister should be abandoned.
He went on: "These are fundamental changes that are being proposed. They cannot be described as tidying up.
"If they fail these tests, then by definition they are negotiating a treaty which will fundamentally shift the relationship between the EU and member states and which will fundamentally change our constitution.
"In those circumstances they should be honour bound to concede a referendum. They should trust the people and let them decide."
The Tory tests include demands that:
the proposed charter of rights should have no legal standing in EU or domestic law
British control over law, border control, asylum and policiing are preserved
defence and security issues should not be consolidated into the EU constitution
Nato's "primacy" over EU defence policy is asserted at the summit and in any future treaty
Earlier this week the Daily Mail newspaper said almost 1.7m people voted in its own "referendum", with nine out of ten people calling for an official referendum on the EU changes.
Critics say the vote is unrepresentative but an ICM poll of 54,971 people for the newspaper also suggests 88% want the vote, with 12% against.
Meanwhile, the Liberal Democrats say it is too early either to rule out or to call for a referendum.
They say they will call for a vote if the final treaty does proposed fundamental constitutional change.