The main Brexit campaign in the EU referendum is adapting tactics in the final phase, as a series of polls suggest that momentum is building up behind the Remain side.
Vote Leave is pursuing a classic core votes strategy to persuade diehard supporters to turn out on 23 June, by focusing on immigration.
The shift in gear came after the campaign spotted what it regards as a path to victory in some of the pollsters' findings.
This is the suggestion that turnout in the referendum could be low, potentially handing an advantage to the Brexit campaign, supporters of which are likely to be more energised to vote.
The Vote Leave campaign knows it must persuade its core voters to turn out.
This explains the recent focus on immigration in speeches and in campaign broadcasts.
Vote Leave insists that nothing has changed and that its campaign had always intended to focus hard on immigration in the final phase.
But earlier in the year campaign sources had said they would not define their campaign on the issue for fear of alienating a key group of voters - encompassing around a quarter of the electorate - who would be wary of a campaign defined by immigration.
Polls commissioned by Vote Leave last year suggested these voters would instinctively like to leave the EU.
But these voters would need reassurance that jobs would be safe and they would not be supporting a campaign associated with UKIP leader Nigel Farage, whose main focus is on immigration.
There is a feeling that Vote Leave has failed to communicate its message about the economic risks of remaining in the EU: the possibility of a Eurozone collapse.
One Brexit minister told Newsnight: "There are jitters in the campaign. I am getting a lot of messages about why we are failing to get our message across.
"Vote Leave does not want to major on immigration, but the problem is that on the economy we are playing defence.
"We are continually having to respond to this tsunami from the Treasury, the Bank of England and the IMF. The only issue we can go on the offensive is on immigration."
Bernard Jenkin, the veteran Conservative MP who supports Vote Leave, insists the campaign is in good heart.
He told Newsnight: "People knew the government would be mean and unfair and promulgate untruths. It will take more than that to wear us down."