Gordon Brown will veto the proposed European Union treaty if it fails to safeguard Britain's no-go areas on further EU integration.
The Prime Minister has dropped his previous threat to call a referendum on the treaty as a means of putting pressure on Britain's EU partners to protect his "red lines" at a summit of European leaders in Lisbon next week. A "no" vote in any EU country would scupper the entire treaty.
Eurosceptics had seized on the threat as a way of securing the referendum for which they are mounting a vociferous campaign.
But British officials admitted yesterday it would be a "non-starter" to call a referendum the Government wanted to lose. Instead, Mr Brown would walk away from the Lisbon summit if the "red lines" were not secured, saying he could not recommend the treaty to Parliament.
Asked if there were any circumstances in which a referendum might be held, Mr Brown replied: "I am a cautious man and I will wait to see the discussion that takes place in the [European] council next week before I make a final judgement. But if we achieve our red lines and achieve them in the detail then we would not need to veto the treaty, we would not need to come back and say the treaty was unacceptable."
He was speaking after talks in Downing Street with Jose Manuel Barroso, the European Commission president, who said: "I believe when people look at the detail of what we have negotiated they will see that the British national interest has been protected, while at the same time the work of the EU of 27 countries can proceed."
The four "red lines", negotiated by Tony Blair at his final EU summit in June, are designed to protect Britain's right to decide its own labour laws; common law, police and judicial system; foreign and defence policy and tax and social security system.
But yesterday, a Commons committee which monitors EU legislationrenewed its warning that the protection offered to Britain by the draft treaty may not be watertight. It told the Foreign Secretary, David Miliband: "The committee has a particular concern over the effectiveness of the safeguards for the UK position on those questions identified by the Government as 'red-line' issues."
Mr Barroso defended the treaty, which will streamline EU decision-making, in a speech in Oxford last night and urged the Brown Government to play a full and positive role in Europe so the EU could maximise its influence in the world.
He said: "Europe needs the UK as much as the UK needs Europe.With your long-held international outlook, I don't believe your arms can be open to the world while your hearts and minds are closed to Europe."
Mr Barroso insisted the treaty did not involve the wholesale transfer of power to Brussels and rejected criticism from Eurosceptics that the EU was obsessed with its institutions. "Those who want to reduce the EU to a market don't even understand markets. You can't run a market stall without rules," he said.
Mr Barroso added: "I find it strange that the debate on this side of the Channel so often seems to suggest the UK is fundamentally at odds with the continent. I don't believe this reflects the reality here in the UK."Reuse content