Britain has signed 'blank cheque' to EU as 31 powers under treaty are yet to be negotiated

A confidential EU paper suggests that the role of the union's president and that of the European police force will not be decided until the treaty is ratified in "difficult" countries such as Britain.

Opponents of the constitution say that signing it now would be equivalent to writing a blank cheque.

The leaked document identifies 31 areas of the Lisbon Treaty where working arrangements are not in place.

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The list includes the powers of a new EU diplomatic service and the extent of co-operation on defence.

Neil O'Brien, of Open Europe, the Eurosceptic think-tank which obtained the document, said Britain would not be able to block any changes made after the treaty is approved.

"Much of the Lisbon Treaty is about giving the EU the power to create new institutions and arrangements and to decide on how they will actually work in practice at a later date," he added.

"Many of these crucial decisions will be made by majority voting, so the UK is unlikely to be able to stop any details it doesn't like the look of. Once the treaty is ratified, there'll be no going back.

"There are so many deliberately unanswered questions in there - about things as important as the role and powers of the EU president and foreign minister - that MPs would effectively be signing a blank cheque to the EU if they ratify this treaty without a referendum."

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The strategy paper was prepared for heads of Government by officials in Slovenia - the current holder of the rotating EU presidency.

It lists the decisions that still need to be taken and identifies "preparatory work" needed during the course of 2008 - when some "difficult" states will still not have ratified the treaty.

Mark Francois, Tory Europe spokesman, said: "This document shows just how dishonest Gordon Brown has been with the British people over this Lisbon Treaty.

"He knows full well it surrenders key powers to Brussels and the leak that controversial decisions are being delayed until after ratification indicates how terrified the Government is that the British people might be given a say in a referendum."

The document says decisions still have to be taken on a range of issues, such as the salary of the new EU president and the powers of the new foreign minister - officially known as the EU high representative - and his diplomatic service.

Other decisions to be taken include how strong defence cooperation should be and what extra powers should be handed to the European police force Europol and the prosecution service Eurojust.

Yesterday Mr Brown again rejected a referendum, claiming the EU treaty was completely different from the EU constitution, which was rejected by voters in France and the Netherlands.

The Prime Minister told BBC's The Politics Show that he had not lied to people by not fulfilling a manifesto pledge for a referendum on the constitution.

"We won all our red lines, and every country in Europe that was planning a referendum, except Ireland, has cancelled their plan for a referendum," he said.