George Osborne has made clear a referendum on the UK leaving the European Union will be a one-off.
The Chancellor told BBC 2’s Newsnight the vote this year, likely in September, would settle the question that has divided the Tory party “for at least a generation”.
Some eurosceptics have suggested two referendums - vote to “leave” and another to potentially to return after two years of negotiations. Boris Johnson was reported to be flirting with the idea.
The comments also underline how the UK Government believes its re-negotiation efforts with European leaders will conclude with a substantial offer of a new deal on control on migration and Britain retaining power over Brussels to voters.
Asked whether the referendum would settle the matter, he said: “You know, I think it will for, you know, for at least a generation, probably for my lifetime.”
He went on: “There’s no second vote. This is the crucial decision of our lifetimes. Do we stay in the European Union, a reformed European Union, or do we leave.”
Speaking in Berlin amid talks with the finance minister Wolfgang Schauble, he said he was “pretty optimistic” an agreement will be struck next month, and “the essential pieces of the deal falling into place”.
He added: “I think we’re also going to be able to deal with the abuse of free movement and people travelling just to claim our welfare benefits”.
The Chancellor also insisted he is not ruling out recommending a vote to leave - pinning hopes of staying in on a reformed EU - and at one point described himself as "a Eurosceptic, like many of my Conservative colleagues" because he wants to make changes.
The remarks came amid a fresh Tory party civil war when pro-EU backbench MP Damian Green attacked “leave” campaigner Chris Grayling for “peddling myths about Britain in Europe”. Cabinet minister Mr Grayling became the first in Mr Cameron’s top team to signal he will vote to leave the EU.