Prime Minister Tony Blair has vowed not to concede Britain's sovereign rights on tax, defence and foreign policy during negotiations on the future of Europe.
Blair: No concessions
The UK's borders would also be safeguarded in a new constitutional treaty expected to be agreed by next spring, he stressed at the EU summit in Greece.
The prime minister and fellow EU leaders formally took delivery of more than 220 pages of proposals for the draft constitution, drawn up by former French President Valery Giscard D'Estaing, on Friday.
The key proposals are for a new full-time president of the EU and an EU foreign minister or foreign policy representative.
But the prime minister made clear the plans negotiated by the convention were just the start.
The summit provided the first opportunity for EU leaders to hold face-to-face discussion on the draft constitution for the union before they meet in Italy in October to begin the process of agreeing a final version.
Mr Blair emerged from the meeting to insist that the UK's demands were being met and that the government's negotiating "red lines" - points which will not
be conceded - would be held.
He said the convention document provided a "good basis" for the inter-governmental conference in October which will discuss it in detail.
"Of particular importance to us is the recognition - expressly - that what we
want is a Europe of nations, not a federal superstate," he said.
Mr Giscard D'Estaing had been hoping the document he presented on Friday would be a definitive new rule book for running Europe, requiring little more than a nod of approval from EU
He called on EU leaders not to unpick the details, but the prime minister stressed that it was up to member states to decide the outcome.
"There are certain issues we have to be very careful about: there is no way Britain is going to give up our independent
sovereign right to determine our tax policy, foreign policy, defence policy and
our own borders," he said.
"There is nothing we will agree to that will put any of that at risk."
But Mr Blair insisted the current proposals reflected most of Britain's views on how the future Europe should look.
"It is important to be welcomed but it is important to recognise that we have our red lines and we are maintaining
them," he said.
The prime minister again rejected the idea of holding a referendum on any new plans for a constitution, suggesting that newspapers were misinterpreting the impact of the proposals.
People would be concerned if they believed what they read in the newspapers, that Britain was giving up the right to set its own defence
and foreign policy and taxation policies, he said.
No such rights had been given up and the European Commission's hopes of taking charge of foreign policy and defence had been "defeated", he said.
But if the expanded EU is to work, changes had to be made, although these did not mean compromising the independent sovereign state in the debate, said Mr Blair.
"I am sure we are going to win it. To marginalise ourselves in Europe would be a huge betrayal."
However, Romano Prodi, president of the European Commission, said he did not want to settle for a weaker commission with more power shifted towards EU member states.
He argued the case for more majority voting, especially on tax and foreign policy, warning that plans for a "President of Europe", answerable to the member states, would duplicate the commission's role and therefore become a rival to the commission itself.
This signalled the start of a future battle between large and small EU
member states over the exact terms of the final constitution.
Mr Prodi sees the commission as the defender of the smaller countries,
particularly when the EU expands to incorporate 25 members.
Tory MP Ian Taylor, chairman of the European Movement, welcomed the draft constitution, stressing: "The publication of the draft constitution has led to the usual predictions about the 'death of Britain' from hardline anti-Europeans ...
"In the face of this onslaught of disinformation, the government has a duty to explain the benefits of European integration in a confident and unapologetic manner."