Boris Johnson has been accused of advocating 'self-destruction' after claiming Brexit will 'unleash' Britain.
The Tory peer also claimed Brexit has become the next 'Western front' in the global fight against Islamic State, warning of 'hostile terrorists' on 'our streets' and warning the leaving EU risks giving a 'nervous minority' a ‘license to kill’.
Mr Johnson wrote in The Sun on Wednesday: 'People are naturally terrified by uncertainty, and this frankly unnerves many politicians.'
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Former Brexit Secretary David Davis told BBC Radio 4's Today programme that Mr Johnson's comments 'smacked of egotism and narcissism'
Rejecting the "generationally dividing rhetoric" he highlighted the 'first generation we've created a de facto border" on our borders in the Republic of Ireland, which is 'quicker and more orderly and has greater confidence than any new arrangement we could put in place'.
And the only way 'to truly preserve our national security and common home will be to retain the tools we have - the single market, the customs union, the European Arrest Warrant', Mr Johnson argued.
His comments echoed those of other Brexit-backing Tory MPs including Anne-Marie Trevelyan, who last week claimed Britain was 'losing our chance to attack Islamic State and other terrorist organisations by sitting on the sidelines of the Brexit negotiations'.
Mr Johnson's comments echoed those of other Brexit-backing Tory MPs, including Anne-Marie Trevelyan, who last week claimed Britain was 'losing our chance to attack Islamic State and other terrorist organisations by sitting on the sidelines of the Brexit negotiations'
Lib Dem leader Vince Cable said Mr Johnson was 'unfit to be a British prime minister'.
He told BBC Radio 4's Today programme: 'Boris Johnson is a political maverick but his demeanour changes just like a clown's does, when he gets used to his position.
'He is already jogging the creation of an illusion that everything is clear as day after so-called expert upon expert tells him so. He is an irrelevance.
'Everybody who really knows has resigned. It's little surprise that very few people follow him. He's unfit to be a British prime minister.
'This latest outburst smacks of egotism and narcissism at the expense of a Prime Minister whose policy is to have done very little. Boris is an exciting demagogue, he doesn't know when to shut up.'
Mr Johnson also predicted that the average income of households in Britain would fall by 3.5 per cent after Brexit, adding: 'Let's be clear: there is no Brexit that won't make things worse.
'If we are now trying to create a new era of prosperity after the ghost of depression, then, while there is little we can say to persuade the richest in Britain - who are already rolling in it - to invest, we also have the choice to start dismantling those institutions and laws that will only help those higher up.'
Mr Johnson predicted that the average income of households in Britain would fall by 3.5 per cent after Brexit, adding: 'Let's be clear: there is no Brexit that won't make things worse'
Mr Johnson added: 'If we think that Brexit will enable the most important decision of our generation to be made in a conclusive manner - think again.
'Some on the Leave side tell us to think again about whether we should leave the EU. But the decision already made by the country would be cast aside for the sake of a short-term reaction.
'I warn against exactly that. Let me say the time to act is now. Because the question of tomorrow's economy should not be decided on this day.'
Meanwhile, former Brexit Secretary David Davis accused Mr Johnson of waging 'one of the more partisan diatribes that I have read since the decision was taken to leave the EU'.
In a blistering editorial in the same paper, the MP for Haltemprice and Howden claimed Mr Johnson was 'poorly advised and badly informed'.
'There is nothing remotely being said in this article that offers any prospect of resolve and potential significant progress in Brussels,' he said.