The British government on Wednesday said the country must remain part of the European Union to protect its economic security and international prospects, but the anti-EU Vote Leave campaign rejected its analysis as "scaremongering."
"The government's clear view is that we are stronger, safer and better off remaining within a reformed European Union," Foreign Secretary Philip Hammond said in a speech defending the analysis.
Continued EU membership would enhance Britain's global influence, give it stronger defences against organised crime and terrorism, and allow better access to a market of 500 million consumers, Hammond said at the Chatham House think tank in London.
"Why would we take that chance with our children's future - risking our influence, our prosperity and our security?" he said of the possibility of voting to leave the EU.
The government's analysis said a British exit, or Brexit, would require bilateral negotiations with the 27 other EU nations that would be "challenging and involve difficult trade-offs."
"It is the assessment of the UK government that no existing model outside the EU comes close to providing the same balance of advantages and influence that we get from the UK's current special status inside the EU," it said.
Speaking for the Vote Leave campaign, rebel cabinet minister Iain Duncan Smith dismissed the analysis as a "dodgy dossier" that "won't fool anyone."
Vote Leave accused Prime Minister David Cameron of "scaremongering" and said a post-Brexit Britain would "get a bespoke free trade agreement with the EU, meaning there will be no tariffs or quotas."
"It's increasingly clear that the real uncertainty is the future of the EU project," said Smith, who is the government's work and pensions secretary.
"As each day passes we see yet another example - from the utter failure to cope with the migrant crisis, to the increasing disaster of the euro," he said.
Cameron earlier challenged Leave campaigners to "set out what their detailed plan for Britain outside the EU is - and its impact on the economy and prices."
The analysis considered three potential post-Brexit models for trade with the EU: a "Norway model" of partial engagement with EU trade treaties; a series of bilateral negotiations with EU nations; and relying solely on agreements via the World Trade Organisation.
Voters in a June 23 referendum are expected to be asked the single question: Should the United Kingdom remain a member of the European Union or leave the European Union?
In the debate over a British exit, or Brexit, Cameron has urged people to vote for remaining part of the EU after he negotiated a deal for reforms that would give Britain a "special status."
A YouGov poll for The Times last week suggested that 38 per cent of people want to leave the EU and 37 per cent want to remain, with the other 25 per cent undecided or not planning to vote.