Brexit: Set out positives of leaving, Boris Johnson urges
Boris Johnson has accused the government of failing to explain how the vote to leave the EU can be made to work in the UK's interests.
He wrote that it could not wait for a new PM to take office in September.
He also said the Leave vote had led to "a kind of hysteria, a contagious mourning" among part of the population.
Meanwhile Foreign Secretary Philip Hammond said it would be "absurd" to say EU nationals can stay in the UK without a deal for UK expats in the EU.
Mr Hammond, who backed Remain and backs Theresa May for Conservative leader, told BBC Radio 4's Today: "I hope we will be able to get to a position where we are able to say to those EU nationals who live in the UK, and to those Brits who live in EU countries, everything's fine, you can stay as you were.
"When you go into a negotiation all the parts are moving, all the parts are on the table, and it would be absurd to make a unilateral commitment about EU nationals living in the UK without at the very least getting a similar commitment from the European Union about British nationals living in the EU."
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Mr Johnson's article in his weekly Daily Telegraph column contains his first detailed comments since he ruled himself out of the race to be the next Conservative leader.
He writes that the Remain side's portrayal of Britain's place outside the EU has led to a "contagious mourning" like that which followed the death of Princess Diana in 1997.
But, he said, the fears of people protesting against Brexit were "wildly overdone".
"The reality is that the stock market has not plunged, as some said it would - far from it," he wrote.
"The FTSE is higher than when the vote took place. There has been no emergency budget, and nor will there be.
"But the crowds of young people are experiencing the last psychological tremors of Project Fear - perhaps the most thoroughgoing government attempt to manipulate public opinion since the run-up to the Iraq War."
Mr Johnson called on the government to come up with a "clear statement" of "basic truths" about leaving the EU.
Among a list of five points of his own, Mr Johnson said it was "overwhelmingly in the economic interests of the other EU countries to do a free-trade deal, with zero tariffs and quotas, while we extricate ourselves from the EU law-making system".
Who's in the running?
Home Secretary Theresa May: The 59-year-old has replaced Boris Johnson as the bookies' favourite to win the contest. She's held the Home Office brief - often something of a poisoned chalice - since 2010, and is a former Tory party chairman. She says she can offer the "strong leadership" and unity the UK needs, and promised a "positive vision" for the country's future. She backed staying in the EU. Theresa May profile
Justice Secretary Michael Gove: The 48-year-old former newspaper columnist was a key figure in the party's modernisation that led to its return to power in 2010. He was a reforming, if controversial, education secretary between 2010 and 2014, and now holds the Ministry of Justice brief. He was a leading player in the Brexit campaign - which put a strain on his close friendship with David Cameron. He has pitched himself as the candidate that can provide "unity and change". Michael Gove profile
Work and Pensions Secretary Stephen Crabb: The 43-year-old was promoted to the cabinet in 2014 as Welsh secretary, and boosted his profile earlier this year when he took over as work and pensions secretary. A rising star of the Tory party he has promised to unite the party and country following the referendum result and provide stability. Raised on a council estate by a single mother, he has a back story to which many Tory MPs are attracted. Backed Remain. Stephen Crabb profile
Energy minister Andrea Leadsom: The 53-year-old former banker and fund manager was one of the stars of the Leave campaign. A former district councillor, she became MP for South Northamptonshire in 2010 and - after serving as a junior Treasury minister and as a member of the Treasury select committee - she was made a junior minister in the energy and climate change department in May last year. Andrea Leadsom profile
Former cabinet minister Liam Fox: It's second time around for the 54-year-old ex-defence secretary and GP, who came a close third in the 2005 leadership contest. His cabinet career was cut short in 2011 when he resigned following a lobbying row. A Brexit campaigner, and on the right of the party, he has said whoever becomes PM must accept "the instruction" of the British people and not "try to backslide" over EU membership. Liam Fox profile
In response, Downing Street said action had been taken to reassure markets and a Whitehall unit would produce proposals for Britain's withdrawal.
Mr Johnson's column did not make any reference to Michael Gove, his fellow architect of the Vote Leave campaign, who has been accused by some of betraying Mr Johnson by running for the party leadership.
Mr Johnson had been the odds-on favourite to become the next leader of the Conservatives but on 30 June announced he did not believe he could provide the leadership or unity needed.
Home Secretary Theresa May has since become the favourite in a contest that also includes Mr Gove, the justice secretary, energy minister Andrea Leadsom, Work and Pensions Secretary Stephen Crabb and former defence secretary Liam Fox.
Meanwhile the campaign manager of Mr Johnson's leadership bid suggested Michael Gove would be a security risk as prime minister, claiming in the Daily Telegraph he had an "emotional need to gossip, particularly when drink is taken".
In his article Ben Wallace MP said: "When I was a government whip and Michael was the chief whip, the office leaked like a sieve.
"Important policy and personnel details made their way to the papers. Michael seems to have an emotional need to gossip, particularly when drink is taken, as it all too often seemed to be."
Asked to comment on the claims, a spokesman for Mr Gove said: "We wish Ben Wallace well."
Elsewhere in the same newspaper, Foreign Secretary Philip Hammond says Mrs May is the person "best equipped to protect our nation's interests in these challenging times".
He says she "has the qualities and the character to take our country forward and, with her quietly determined, down-to-earth style, to re-unite us after the referendum".
Speaking to BBC Radio 4's Today programme, one of Mrs Leadsom's backers, Anne Marie Morris, said the former investment banker was someone "extremely well placed to negotiate the Brexit exit".
Who's backing who?
Asked whether Mrs Leadsom's six years as an MP and two years as a junior minister gave her enough experience to be prime minister, Ms Morris said: "I don't believe Andrea is a novice.
"What we have to look at is the importance of having some real life business experience... she is a hard lady and will absolutely drive the country forward."
Meanwhile, senior Leave campaigners are calling for the UK to exit the EU by Christmas through an act of Parliament.
Writing in City AM, former Chancellor Nigel Lawson and ex-Labour foreign secretary David Owen press for the next prime minister to leave the bloc without waiting to trigger Article 50, which is used to formally pave the way for a two-year withdrawal process.
They are being backed by a number of pro-Brexit Conservative MPs alarmed that the process could take years and suggestions from some Tory leadership contenders that they would delay triggering Article 50.
"We owe it to the British people to deliver on the referendum vote and not to cavil or delay. That means starting to leave in a few months, not stretching it out for years," they write.