Tory 'Leave' campaigners Justice Secretary Michael Gove and Boris Johnson have issued a stark warning to David Cameron that his credibility is on the line over EU membership, and his failure to limit migration is "corrosive" to public trust.
In a joint letter, published in the Sunday Times (£), they wrote: "There is also the basic lack of democratic consent for what is taking place. Voters were promised repeatedly at elections that net migration could be cut to tens of thousands.
"This promise is plainly not achievable as long as the UK is a member of the EU and the failure to keep it is corrosive of public trust in politics."
Mr Gove has also written to the prime minister urging him to tell the truth about the impact of staying in the EU, The Sun on Sunday reports.
He said Mr Cameron's "apocalyptic warnings" on Brexit would test his credibility if they turned out to be false.
Mr Gove also ridiculed the prime minister's insistence that Turkey was not set to join the EU, saying that this was the latest in a series of "lies" regarding EU membership.
The justice secretary insisted that every citizen needs to be aware of the "real risks" of remaining in the EU, and hit back at claims that the Leave campaign is fuelled by prejudice.
"When people fling the charge of racism, what they are actually doing is attacking working-class people for wanting to maintain a decent standard of living - I think that's wrong," he said.
Meanwhile, employment minister Priti Patel has attacked those leading the Remain campaign with "luxury" lifestyles of being too rich to care about people's concerns regarding migration.
Conservative MP Andrew Bridgen has also criticised Mr Cameron, insisting he is "finished" as Tory leader because of the way his "Operation Fear" tactics have divided the party.
Number 10 said the Brexit attacks were an attempt to "distract" from a survey of 600 economists showing 88% believed withdrawal would be damaging for the economy.
Labour former prime minister Tony Blair has issued an appeal to undecided voters considering Brexit: "If you're not sure, don't do it."
He made the comments, as he wrote in The Sunday Times that withdrawal would be a "betrayal of British interest".