LONDON: Eurosceptic Tory leader David Cameron will pledge on Wednesday to wage battle with the European Union if, as expected, his party wins next year's general election, reports said.

Cameron will officially announce he is dumping plans to call a referendum on the EU's Lisbon Treaty if the Conservatives take power next year.

The policy U-turn comes after Czech President Vaclav Klaus became on Tuesday the last EU leader to sign the landmark document into European law.

"Now that the treaty becomes European law, a referendum can no longer prevent it," the party's foreign affairs spokesman William Hague said.

But in an attempt to appease eurosceptics within his party, Cameron is set to declare he is prepared for tough relations with the EU -- that could include a referendum on any future treaty that transfers power to Brussels.

He will also pledge to negotiate opt-out clauses on key EU policy areas such as social and employment powers, according to the Daily Telegraph.

Cameron, who holds a substantial lead over Prime Minister Gordon Brown in opinion polls, is also set to reiterate his party's commitment never to join the euro, the Financial Times said.

The pledges could cause headaches for the European Union if the Conservatives sweep to power at the general election due by next June.

Newspapers said it was unclear if Cameron's speech on Wednesday would stymie anger among hardline Conservative eurosceptics who accuse him of breaking a "cast-iron" guarantee made in 2007 for a referendum on the Lisbon Treaty.

Cameron for months declined to be drawn on what he would do if the treaty is ratified by all 27 European Union member states.

He drew criticism last month when it emerged he had written to Klaus stating that the Conservatives would hold a referendum if he took office and the treaty was not yet in force.

Polls indicate such a referendum would result in a No vote in strongly eurosceptic Britain, which is not a member of the eurozone single currency bloc, or of the Schengen open borders area.

The front-page of The Sun on Wednesday declared: "Signed. Sealed. Delivered. Up Yours!"

"Britain betrayed as hated EU treaty is finally made law."

The Lisbon Treaty is designed to streamline the running of the bloc, which has almost doubled in size to 27 nations since a swathe of ex-communist countries including the Czech Republic joined in 2004.

Brown, languishing in popularity polls two and a half years after he succeeded Tony Blair, on Tuesday welcomed Klaus's signature as "an important and historic step for all of Europe".