Employment Minister Priti Patel has launched a scathing attack on the "chaos" of Britain's immigration controls.
The pro-Brexit Conservative MP said immigration is "uncontrolled and uncontrollable" while Britain remains in the EU.
Writing in The Sun newspaper, Ms Patel commented: "There is another great bonus of leaving the EU - we'll be able to design a new immigration system that brings the chaos under control and helps the economy.
"It is running at the rate of a million every three years. Last year, 270,000 arrived from Europe alone."
Ms Patel also criticised economic predictions from government colleagues in the Treasury about what could happen in the event of a withdrawal from the EU.
"If the government seriously believed the doom-laden propaganda they have been pumping out about the horrors of life after the EU, they would never have called this referendum in the first place," she said.
Ms Patel's comments come after figures released by the Office for National Statistics reveal that net migration to the UK rose to 333,000 in 2015 - the second highest figure on record. The figure for EU-only net migration was 184,000.
The Treasury meanwhile, warned that pensioners could be thousands of pounds worse off if the UK votes to leave the EU.
Ministers said Brexit would cause inflation to rise and erode the value of state pension increases.