David Cameron's EU speech will hand the British people the chance to give their "fresh consent" to the UK's relationship with Brussels, William Hague has said.
The foreign secretary said Britain wanted changes in its relationship with the European Union but that the UK needed to monitor how changes in the eurozone affected the EU before making a final decision.
He told BBC1's The Andrew Marr Show: "When we have done those things, there is a case for [seeking] fresh consent… for that in its modern form, in the best form that we can bring about."
Cameron's speech, set for last Friday in Amsterdam, was postponed as the Algeria hostage crisis developed. It is now expected to take place in Britain in the middle of the coming week.
Extracts already released show the prime minister is set to call for a referendum at some stage in the next parliament.
Labour has suggested the Conservative party leadership is pursuing a referendum for party political advantage as strategists begin to look to the 2015 election.
"It's about doing what's best in the interests of this country, and also about democracy in this country," Hague added.
Questions are now focusing on whether the vote will effectively be on Britain's continued membership of the EU.
Pressure from Eurosceptic Tories has intensified in recent months alongside steady improvements in Ukip's standing in national opinion polls, which is now close to double figures.
Ukip leader Nigel Farage told the same programme: "What is really happening is that we will get the speech and then the Conservatives will launch a five-year campaign to try and keep us in the EU.
"It is all reminiscent of 1975 when Harold Wilson came back with a cosmetic renegotiation and put it to the country."
Hague said he wants to see Britain succeed in the EU but said the union had "changed a lot since the referendum of 1975".
The Tory leadership is unlikely to completely satisfy opinion on its backbenchers.
Many hardline eurosceptics are demanding that the government legislates to guarantee a referendum in the next parliament.
Others, including Bernard Jenkin, want to hold a referendum now giving the UK government a mandate to hold a renegotiation.
Jenkin told the Sunday Telegraph newspaper: "The least we owe the PM is to hear the whole of his speech - but the question which continues to nag is whether anything promised in this parliament can settle the debate as effectively as a clear statement in a manifesto referendum about what sort of relationship in with the EU that we want."
Former defence secretary Liam Fox, who wants a call for a return to the common market to be the centrepiece of the Conservatives' next general election campaign, told BBC1's Sunday Politics programme he had been briefed on Cameron's speech.
"I'm broadly satisfied with what I saw that the prime minister was intending to say," he said.
"And I think if that is the speech that is finally delivered, a great many of us will think that it's a speech that we've been waiting a long time for any prime minister to deliver."