Michael Gove has insisted the Leave campaign's proposals to introduce an Australian-style points-based immigration system would "liberate" David Cameron and allow him to deliver a Tory manifesto commitment.
Mr Gove, Boris Johnson and Priti Patel have outlined an immigration blueprint which would end the automatic right of European Union (EU) citizens to come to live and work in the UK with migrants only allowed in if they meet certain skills criteria.
And the Justice Secretary believes the plans would help the Prime Minister deliver a Conservative Party manifesto pledge to reduce immigration to the UK to the "tens of thousands".
However, Mr Gove's comments, made during a Vote Leave battle bus tour of Lancashire, come after the proposals were slammed by George Osborne as "fantasy politics" and as Tory Cabinet divisions over the referendum grew still further.
The Chancellor also suggested the measures could actually lead to an increase in immigration.
But Mr Gove said Mr Cameron will be unable to meet the party's election pledge on immigration unless the UK votes to leave the EU on June 23.
"The only way he can fulfil it is if we leave the European Union," he said.
"He's the Prime Minister, he sets policy, he will set policy after June 23 but we want to liberate him to be able to fulfil the manifesto pledge on which he stood."
Mr Johnson and Ms Patel visited a clothing factory in Accrington to bang the drum for Brexit before being joined by Mr Gove to deliver stump speeches to a large crowd in Preston city centre.
And Mr Johnson claimed during his speech that "the big difference between them (Remain) and us is that they don't believe in this country".
The former mayor of London was asked on numerous occasions during the tour whether Leave's immigration plans actually amounted to a pitch for an alternative post-Brexit government.
But he rejected the idea.
"No," he said. "We are not forming an alternative government, we are presenting alternatives to the government."
Meanwhile, Mr Gove said the Leave campaign was simply aiming to provide the Government with the "means" to fulfil its manifesto promises.
"We want to allow the Prime Minister to be able to fulfil the pledge on which he stood," he said.
"At the moment the Prime Minister cannot fulfil that pledge as long as we are in the European Union.
"If we leave the European Union he can."
Mr Johnson said it was "iniquitous" that the UK can currently "discriminate very heavily against talented people coming from outside the EU".
Meanwhile, there is "absolutely no way of stopping people from coming into this country even if they have a criminal conviction, a very serious criminal conviction from other European countries".
Ms Patel said the immigration proposals are not about hitting a specific target number of people coming to the UK.
Instead, they are about introducing "fairness" and "meritocracy" to the system.