The Czech Cabinet meets in emergency session today to consider how to persuade their stubborn President to sign the Lisbon treaty — under intense pressure from Paris and Berlin to complete the ratification as soon as possible.

With President Klaus demanding a last-minute amendment as the price of his signature — the final approval required in the 27-nation European Union — the Government is locked in a trial of strength with its head of state and on the brink of a constitutional crisis. If it supports his demands the treaty might have to be reopened amid lengthy delays, possibly allowing time for David Cameron’s Conservatives to win the next British election and hold a referendum on the treaty as they have promised.

If the the Czech Government opposes President Klaus then it may have to resort to a form of impeachment or strip him of his treaty-signing powers so as to complete ratification.

Barely disguising the anger felt in European capitals, Fredrik Reinfeldt, the Prime Minister of Sweden, which holds the EU’s rotating presidency, told a signing ceremony by Poland that Czech assent was eagerly awaited. He added: “We do not need more delays.”

France and Germany, which claim the credit for reviving the treaty after the draft EU constitution collapsed in 2005, are furious but wary of putting overt pressure on President Klaus, who has a habit of reviving wartime passions to rouse popular support.

He has said that he wants an opt-out from the charter of fundamental rights, a key part of the treaty, because he fears that it could give Germans expelled from the Sudetenland after the Second World War the right to take property claims to the European Court of Justice. EU officials point out that Britain and Poland negotiated their own opt-outs from the charter while the treaty was being discussed in 2007 and suggest that it is a delaying tactic from President Klaus — a strong Eurosceptic who often compares the EU to the Soviet Union — while he tries to give Mr Cameron time to get elected and carry out his referendum pledge.

Mr Cameron encouraged the President’s delaying tactics in a letter this summer. The Conservatives are refusing to release the text but insist that Mr Cameron simply set out the party’s policy of holding a British referendum on the treaty if it remains unratifed somewhere in the EU should they come to power. David Miliband, the Foreign Secretary, has written to William Hague, his Tory shadow, demanding that the letter be made public.

President Klaus’s chief political adviser, Ladislav Jakl, underlined his resolve yesterday. “If the Czech Republic does not get the opt-out, the President will not ratify,” he said.

The Czech Government is in a weakened position after the ousting of Mirek Topolanek, the Prime Minister, and his Civic Democratic Party in May and his replacement with a caretaker Cabinet of non-partisan civil servants.

Czech constitutional experts set out several options before today’s Cabinet meeting in Prague. The Government could ask the constitutional court to decide whether the President has the power to submit demands. It could also propose that parliament change the provision in the constitution that says who signs international treaties.

It could also ask parliament to state that President Klaus is no longer competent to exercise the post of President. Or it could propose that the senate brings a lawsuit against President Klaus for conduct against the democratic order of the Czech Republic.

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