Britain will face annual net migration of over a quarter of a million for the next twenty years if the country remains in the EU, according to a report from Migration Watch released today.
The report describes its findings as a "cautious estimate", saying that net migration could be 265,000 in 2035. Sixty per cent of this would come from the EU, and the report "notes that there is widespread complacency and denial about both the likelihood and the impact of rapid population growth".
James Brokenshire, the government's immigration minister who is pro-EU, said that leaving the EU was "not the answer to the complex issues of immigration".
Lord Green of Deddington, chairman of Migration Watch UK, said: "This report is a final wake up call. Even leaving aside the prospect of Turkey joining the EU, it shows that net migration could still be running at 265,000 a year in 20 years time.
"This would bring our population to 80m within 30 years. If we remain in the EU there will be nothing to stop a continuing rapid increase in our population.
"This would change our country for ever against the express wishes of a very large majority of our fellow citizens."
The report comes as the issue of Turkey joining the EU has become a hot-topic in the debate, with Ian Duncan Smith saying the government is "perpetuating an enormous deceit on the British public" over visa-free travel for people from Turkey.
Brokenshire said: "David Cameron is in complete agreement with the leaders of the Leave campaign who have admitted Turkey joining the EU isn't remotely on the cards.
"Damaging the economy by quitting Europe is not the answer to the complex issue of immigration. Migration Watch say the Leave campaign's policy won't work - it could actually increase immigration.
"Independent experts agree that leaving Europe would hit the economy - costing jobs, putting up prices and meaning less money for the government to spend on public services like the NHS."