Prospects of a deal on the future of Europe at Tony Blair’s final summit are threatened by fears that a rash of demands for opt-outs from EU laws will turn the negotiations into a farce.

Allies of Gordon Brown are privately insisting that Mr Blair’s desire for an agreement as he heads out of office must not stand in the way of Britain blocking the whole proposed treaty if it has objectionable elements.

The Prime Minister, supported strongly by the Chancellor, is pressing for Britain to have legally binding exclusions from any plans to end the veto on issues affecting justice and home affairs and the social security treatment of migrant workers.

They also oppose the proposals of Angela Merkel, the German Chancellor, to bring back the charter of fundamental rights that was included in the proposed constitution that was rejected by referendums in France and the Netherlands.

At the least, Britain is seeking watertight legal assurances that the charter could not apply in Britain and could not be used in cases against this country in the European Court.

Senior ministers say that Britain’s demands will inevitably be matched by other countries asking for opt-outs on areas of the treaty that they find unacceptable; and there are signs that others intend to take a hard line at the European Council gathering in Brussels on June 21 and 22 for their own domestic reasons.

Insiders close to the negotiations say that they have been perplexed, for example, by demands from Poland that the EU must be explicitly defined as a “Christian entity”, a move that could be used to block Turkey’s eventual accession.

Insiders say that the Dutch are more worried than Britain about the EU signing up to anything that might require a referendum. “Their bar for a referendum is even lower than ours, and they fear they would lose it again, so that would help nobody,” the source said.

President Sarkozy of France has made plain to Mr Blair that he will back an opt-out for Britain if the EU decides to end the veto on justice and home affairs issues. But he is keen to end that veto because of French reverses in the European Court at the hands of what he sees as excessively liberal legal opinions.

At their meeting at the G8 Mr Blair and Mr Sarkozy agreed that it should be an “amending treaty” that would not require referendums. But that will not be the view of the Conservatives or Labour Euro-sceptics if there is any transfer of power to the EU.

Mr Blair is fighting against a new plan for the system of qualified majority voting (QMV) to be adopted for matters relating to the social security treatment of migrant workers. Backed by Mr Brown, he is proposing that Britain should be able to play a “joker card” so that whenever it objected to a matter being handled under QMV it could demand that it go before the full European Council heads of government, where the usual unanimity rule would apply. Britain would therefore keep its veto by other means.

The Times has been told that Mr Brown is keeping a close interest in the negotiations and has not disagreed with the way Mr Blair is handling them. He is nervous, however, of showing his detailed hand, to prevent negotiators using claims that he will be tougher than Mr Blair as a factor in coming to a deal. An ally of Mr Brown said that, whatever came out of the summit, Mr Brown would have to take it forward. “We cannot have a deal at any price just because Tony is going. We can only allow through now what will be defensible down the line.”

Division points

— Charter of Fundamental Rights

— Veto on home affairs

— Social security and migrant workers

— No big changes without referendum

— Britain wants “amending treaty” only

— Blair “must not give too much”

Times Recommends

• Plan for 9/11 trial in New York divides the city
• Beijing gets the jitters as Obama flies in
• Potshot Palin settles scores