Gordon Brown looked set last night to secure Britain's "red lines" on the new EU treaty but was facing an intense backlash from political opponents demanding a UK-wide referendum to decide the issue.

As two polls suggested seven out of 10 Britons wanted a vote on the proposed changes to how the EU is run, the Prime Minister held the UK Government line that a referendum was not necessary because the new treaty simply amended previous agreements and so was not the draft constitution rejected by the French and Dutch in 2005.

Before a dinner with his European counterparts in Lisbon, Mr Brown told a press conference at his first EU summit as PM: "At every point we have been determined to protect the national interest and ensure the interests of British people are safeguarded."

This, he argued, was represented by the government's "red lines", guaranteeing opt-outs on key areas covering UK foreign policy, social policy, justice, security and employment law.

He insisted the EU had to "move on from inward-looking discussion" to focusing entirely on economic and social change to create "better jobs, higher security, action against climate change".

Mr Brown declared: "These are the issues people want us to address."

As the talks got under way, Angela Merkel, the German Chancellor, was cautiously optimistic saying she expected "difficult" talks to clinch an overall deal but noted how the leaders were "now just a few millimetres from the finish line".

Earlier, Jose Manuel Barrosos, President of the European Commission, made clear Britain's "red lines" should be respected but insisted the UK should not make any more demands at the summit.

"Of course, we regret that it was necessary to have some opt-outs from some countries but we respect this. We prefer to have a solution that is broadly agreed with some specific opt-outs for some countries than not to move forward."

The EC chief said Britain had negotiated "very hard" to secure its opt-outs on specific issues but declared: "Now we don't expect any more requests in that area." He added: "I hope we will have a consensus today or tomorrow on the reform treaty."

Like the previous Constitutional Treaty, the Reform Treaty is designed to streamline EU decision-making and avoid inevitable bureaucratic gridlock as the 27-strong union expands to include more member states.

However, the search for a deal has triggered Eurosceptic warnings that the exercise is simply an excuse to push for a federal Europe.

In the Portuguese capital, Mr Brown was not alone in threatening to block agreement unless he got what he wanted from the summit; the Poles were warning they must have better EU voting strength, the Italians wanted more MEPs in the proposed slimmed-down European Parliament while the Bulgarians want to be able to use the Cyrillic version of the word for the "euro" in official EU documents in future.

Any one of these issues could scupper the summit talks but Mr Brown's "red lines" were effectively agreed before the summit started. Yet, one official cautioned: "As always on these occasions, nothing is agreed until everything is agreed."

On Monday, the Prime Minister is due to face his critics when he gives a Commons statement on the summit. It is expected to be a heated affair.

Last night, the Tories vowed to intensify their campaign for a referendum. William Hague, the Shadow Foreign Secretary, launched a stinging attack on Mr Brown, saying he was "still treating the British people like fools" and that his "spin has reached new depths of cynicism".

He argued it was little wonder that every poll showed that the vast majority of the British people wanted a referendum and did not believe his arguments.

"His spurious red lines' do not cover most of the renamed EU constitution and can easily be got round. Now that all his arguments against a referendum have crumbled he is desperately trying to change the subject."

The former Tory leader added: "Gordon Brown bottled out of a General Election. Now he won't listen to voters on Europe either. Why should they trust him when he so clearly does not trust them?"

Meanwhile, Mr Brown said last night he would discuss the case of missing Madeleine McCann with his Portuguese counterpart, Jose Socrates, at the summit.

He told reporters: "I'm meeting the Portuguese prime minister later and we will discuss this issue. I have discussed this issue with him before, to assure myself that the police authorities are taking the actions that are necessary and there's proper co-operation between the British and Portuguese police."

Mr Brown has received regular briefings on the case since Madeleine's disappearance on May 3.

As well as keeping himself up to date on the details of the police investigation, Mr Brown has spoken to Gerry McCann several times.