Theresa May to formally rule out membership of the Single Market after Brexit in a move that has been described as a “hard Brexit”.
Vice chairman of Migration Watch UK said: ““This research spells out the very serious consequences for our society of net migration continuing at its present scale with membership of the single market resulting in a relentless increase in our population.
“An increase of anything like 12 million in just 25 years is, quite simply, unacceptable to the British public and certainly not what they voted for in the referendum.”
The most recent official figures showed that total international net migration – the difference between the number of people arriving and leaving the country – was at a near record estimated level of 335,000 in the year to the end of June.
The paper from Migration Watch suggests that net migration, including both EU and non-EU migrants, is likely to remain at more than 300,000 in the medium to long term unless Britain leaves the Single Market.
Net migration from the European Union alone will remain at 155,000 as migrants are drawn to Britain by the prospect of higher wages and more jobs.
The report found that the UK’s minimum wage remains three times higher than that of Poland, five times higher than in Romania and six times higher than in Bulgaria.
Migrants will also continue to be attracted to Britain because of the high rates of youth unemployment in Southern Europe.