GORDON BROWN is insisting he will not be bound by any new European Union constitution and that Britain must have opt-outs from key elements if any treaty is agreed at a summit of EU leaders at the end of this month.

The chancellor, who will take over as prime minister a few days after the event, has emphasised in private talks with Tony Blair in the past fortnight that he will not be tied to any deal made if it involves surrendering more powers to Brussels.

Brown and Blair have agreed Britain must have opt-outs or, failing that, block the whole deal if other member states wish to press ahead with the plans of Angela Merkel, the German chancellor, to make legally binding a new charter of fundamental rights and remove the national veto on justice and home affairs.

Nicolas Sarkozy, the French president, who embarrassed Blair by revealing at last week’s G8 summit that “Tony Blair and I have just agreed on what might be the framework for a simplified treaty”, wants to meet Blair and Brown in London this week. He wants to hear their demands for a watered-down “amending treaty” that would allow a rebalancing of voting rights in light of the expansion of the EU to 27 states, without surrendering any British sovereignty.

The prime minister in waiting wants to ensure that any agreement does not threaten to erode such sovereignty and spark demands for a referendum in this country. Such a plebiscite, he believes, would be a gift to David Cameron’s Tories. “Any treaty that is about the transfer of powers to the EU must be put to the country in a referendum,” Cameron has said.

One of the controversial aspects of the German plan that Brown has told Blair he must resist are proposals to make a charter of fundamental civil and labour rights legally binding. This could threaten Britain’s laws that ban closed shops and secondary picketing and that require ballots during industrial disputes.

Another problem is a plan to end the national veto on Europe-wide justice and security policies, which UK officials fear may wreck police powers to hold and question terror suspects.

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