Tory leader Michael Howard says his party will hold an early referendum on Europe if it wins the next election.
Michael Howard: Vote Lib Dems or UKIP to get another Labour term
Seeking to win back voters from the UK Independence Party, Mr Howard said a referendum could be held by October 2005.
In a wide-ranging interview with the Daily Telegraph, Mr Howard said he wanted to "start bringing back powers to Britain from Brussels".
The Tories came fourth in the Hartlepool by-election on Thursday.
Labour won, followed by the Liberal Democrats and then UKIP.
Mr Howard said a vote for any of the smaller political parties was effectively a vote for Labour.
"It is very simple," he told the newspaper. "If you want another Blair government, vote UKIP or Liberal Democrat."
Mr Howard said the Tories would fight to reject the proposed European Constitution if they won the next election.
"I will campaign for a No vote," he told the Telegraph.
"I am confident we will get a No vote. I will then go to the EU with a double mandate - a general election mandate and a referendum mandate.
"I would say we are against the constitution. The constitution is dead."
Speaking before his party's annual conference next week, he said: "Let us sit down and look at the things that Europe can do best and nation states can do best.
"And let us start to accept there are many things that history shows very clearly are now much better dealt with at national level rather than European level.
"I am fed up with the state of affairs where Britain is always saying `no' to the countries of Europe.
"So let's reach an agreement - you can do what you want to do. And if you want to integrate more closely, that's fine by us - as long as you don't make us do what we don't want to do."
In the interview, Mr Howard also discussed Tony Blair's treatment of intelligence in the run-up to war in Iraq.
He said Mr Blair had not told the truth about Saddam Hussein's alleged weapons of mass destruction.
"Mr Blair said the assessed intelligence had established beyond a doubt that Saddam had continued to produce chemical and biological weapons," he said.
"The Joint Intelligence Committee said it had little intelligence on Iraq's
chemical and biological doctrine and knew little about those weapons since
Turning to his party's policy on tax, Mr Howard said they would avoid Labour's
"third-term tax rises" by slowing government spending.
He said the Tories would offer "targeted tax cuts", but refused to rule out
rises in tax.
"I am not going to make promises I can't keep," he said.
Mr Howard added that inheritance tax was an unfair levy while stamp duty
discouraged people from buying their own homes.