David Cameron's former policy guru has claimed the Prime Minister was told four years ago it was "impossible" for the Government to meet its immigration promises if the UK remained in the EU
Leave supporter Steve Hilton said civil servants "directly and explicitly" explained the pledge to reduce net migration - which last month hit 333,000 - to the tens of thousands would fail.
Just weeks ago, Mr Cameron insisted he stuck by his "ambition" to pull the number under 100,000.
But Mr Hilton said the premier reaffirmed his commitment to target in the 2015 general election even though he "had been told it was undeliverable".
Writing in The Daily Mail, the Leave campaigner recalled the details of a meeting in the final months of his time as director of strategy.
He said: "We were told, directly and explicitly, that it was impossible for the Government to meet its immigration target as long as we remained members of the EU, which of course insists on the free movement of people within it.
"In the 2015 Conservative manifesto, the Prime Minister reaffirmed his commitment to the immigration target he had been told was undeliverable.
"When I saw that, I assumed this was either because he was certain he could negotiate a solution within the EU, or was assuming we would leave."
It comes as research for The Daily Telegraph said the In camp was seven points ahead, with 53% of the vote among those who intend to have their say at the ballot box.
But the ORB International study found that when all voters are taken into account, the Remain lead drops to two points on 49%, compared to 47% for Leave.
Exit poll supremo John Curtice, a professor at Strathclyde University, said the possibility of the UK quitting was being underestimated, suggesting a 45% probability was a "sensible" assessment.
Additional reporting by agencies
