In an escalation of the Tory civil war, Johnson, who has been posing increasingly as a prime minister in waiting, told the Observer that he believed no genuine “liberal internationalist” could support the EU.
In a separate statement, justice secretary Michael Gove said that it was outside the EU that the “progressive, one nation policies” the prime minister professed to support would become a reality. The Tory cabinet minister added that the EU worked only in the interests of the bankers, corporate giants and “undeserving rich”.
Labour leader Jeremy Corbyn dismissed the claims and said “Tory Brexit” was a threat to workers’ rights. He said: “I just don’t believe them when they say they want to leave the European Union to bring about social justice.
“Who has suffered the price of austerity? 80% of the cuts have hit women. Who has been hit the hardest? The disabled.
“They are backed by hedge funds and others that envisage an economy which is an offshore economy of low tax, high profits, low wages.”
Labour peer Lord Mandelson, the former business secretary, said: “In my lifetime, there has been no greater threat to this country than a disastrous combination of leaving the EU and a Boris Johnson premiership.”
The row comes as the latest Observer/Opinium poll gives the leave campaign (43%) a three-point lead over remain (40%), who are down four percentage points from two weeks ago.
Responding to the poll, the shadow chancellor, John McDonnell, on Saturday made the dramatic warning that Cameron and George Osborne were “blowing it”.
In an interview with the Observer, he called on the Conservatives to “back off” from the campaign or condemn the UK to Brexit.
He said: “I think it [the referendum race] is close, and I think the reason it is close is that this establishment campaign is blowing it.
“I just think the strategy needs to change in the remain campaign. I think people are where I am, which is, yeah, a Eurosceptic position – but not a Euro exit position.”
McDonnell added: “I think a period of quietude from the likes of Cameron and Osborne and others would be helpful. It has to be a positive campaign from here on in. And I am saying to Cameron and Osborne that it is time for them, the elite, to back off.”
The Tory cabinet minister, Chris Grayling, who is backing Brexit, also suggested that Vote Leave was on track for victory.
He told the Observer: “I have been cautiously optimistic from the start, but having gone through the last three weeks, and the purdah period, there is a slightly different mood around. It is tangible. It feels like people are starting to make their mind up and they are making their mind up our way. I wouldn’t overstate that, but it does feel things are moving in our direction.”
Grayling said that, while he was a “rightwing Conservative”, that he also believed that leaving the EU would allow Britain the power to be genuinely “one nation”.
The leader of the House of Commons, Grayling said: “The battle to leave the EU is not about destroying workers’ rights in the UK. I am someone who believes that a well-supported workforce is essential in today’s world for good economic performance.
“We want a society that gives people real opportunities and I think [leaving the EU] enables us to step towards being more of a one-nation country.
“It is not just about migration pressures, but we have much more control of what happens.”
In support of the claims, Johnson said the EU’s common agricultural policy had hit farmers in the developing world while the euro had crippled Greece. The former London mayor added: “The impact of EU-enforced uncontrolled immigration to the UK – made worse by the euro crisis – has been to depress the wages of the low-paid, while fat cat FTSE-100 chiefs have seen their pay packets soar to 150 times the average pay of their workforce.
“It is time that liberals everywhere saw the EU for what it is – essentially a stitch-up between the very biggest corporations, their lobbyists and the commission to frame regulation in such a way as to keep out the competition, especially … from start-ups and innovators,” he said.
“That is one of the reasons – along with the euro – why the EU is a zone of low growth, low innovation, and very high unemployment.
“It makes no sense to stay in this unreformed EU, and only Brexit can shake it up.”
Gove said in his statement to the Observer: “The EU works for big banks, multinationals and the undeserving rich.
“They spend millions lobbying bureaucrats in Brussels to rig the rules in their favour. It is clearly in their interests that we remain.
“Leaving the EU would liberate us to invest in public services and support struggling communities.
“We could also supercharge support for education and science. Outside the EU we could more easily fulfil our shared ambition to have progressive, one-nation policies.”
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