Boris Johnson first became associated with Euroscepticism in the early 1990s, when he wrote a string of articles for the Telegraph lampooning apparently over-zealous EU regulations.
Now he could be the Prime Minister who pulls Britain out the EU without a withdrawal agreement.
But there have been many contradictions and changes of heart along the way. Boris Johnson once said he was “a bit of a fan” of Brussels, and he famously wrote an unpublished column declaring his support for the remain campaign.
What else has the PM said about Europe over the years?
‘Worrying loss of influence’
In his 2001 book ‘Friends, Voters, Countrymen’, written while he was trying to win a seat in the Commons for the first time, Mr Johnson wrote that Britain’s interests were “still on balance served by maintaining our membership” and said withdrawal would mean “a worrying loss of influence”.
In 2003, he told the House of Commons: “I am not by any means an ultra-Eurosceptic. In some ways, I am a bit of a fan of the European Union. If we did not have one, we would invent something like it.”
In the same debate he looked forward to the expansion of the EU, adding: “I do not know whether any honourable Members are foolish enough to oppose eventual Turkish membership of the European Union.”
Compare that to the Vote Leave campaign that Mr Johnson helped run in 2016, which was criticised for running advertisements warning about mass immigration if Turkey was allowed to join the bloc.
In or out?
As late as February 7 2016, Boris Johnson was still talking about “deciding how to vote” in the upcoming referendum, arguing that it was in “Britain’s geostrategic interests to be pretty intimately engaged” with Europe and warning that leaving the single market would cause “at least some business uncertainty”.
He finally revealed that he was backing leave in another Telegraph column on 21 February. It later emerged that he had secretly written an alternative version of the article in which he reluctantly backed remain instead.
Mr Johnson said he wrote the unpublished version as a mental exercise, calling it “semi-parodic”.
But just a few months earlier, in 2015, he said: “I think that there is a very valid future for this country not in the EU. It’s not my preference, because there are some downsides.”
The single market
“We are – and we will remain – a paid-up, valued, participating member of the Single Market,” Mr Johnson said in 2011. “Under no circumstances, in my view, will a British government adjust that position.”
By 2012 Mr Johnson was calling for a referendum on Britain’s place in Europe – but a rather different poll from the one we finally got.
His suggestion was that the government should negotiate a minimalist relationship with Brussels and put the question to voters.
He said that if there was a public vote, he “would be well up for trying to make the positive case for some of the good things that have come from the single market”.
In December 2012 Mr Johnson told an audience of business leaders that Britain could “construct a relationship with the EU that more closely resembled that of Norway or Switzerland”. Both those countries are members of the single market, but have to make financial contributions to the EU budget and accept the free movement of workers from other member states.
In an interview with Sky News in 2013 he said: “I’d vote to stay in the single market. I’m in favour of the single market.”
The same year he also said he believed the “overwhelming majority of people” want to remain “firmly in the Single Market”.
During the 2016 referendum, Mr Johnson and other Vote Leave campaigners were hard to pin down on whether they wanted to negotiate continued membership of the single market after Britain left.
But immediately after the referendum, he said Britain would still “have access to the single market”.
This echoed a vague form of words that fellow Vote Leave campaigner Michael Gove had used in the campaign, before he was finally forced to admit that the UK would in fact have to leave the single market.
In early 2018, as Theresa May was negotiating a withdrawal agreement with the EU, Mr Johnson’s allies were briefing reporters that he was concerned the Prime Minister would allow Britain to drift into a Norway-style “soft Brexit” and that this would be “mad”.
Theresa May’s deal
Boris Johnson was a bitter opponent of the Chequers deal negotiated by his predecessor in Downing Street, controversially calling it a “suicide vest” around the British constitution.
He said the withdrawal agreement would lead to the EU becoming Britain’s “colonial masters”, and wrote in his Telegraph column that there was “no way” he would vote for a Northern Ireland backstop.
In the end Mr Johnson voted against Theresa May’s bill twice, only to change his mind and vote for it the third time, saying he had reached the “sad conclusion” that it was the only way to ensure Brexit.
EU citizens’ rights
In the referendum campaign Mr Johnson signed a public pledge which said that “EU citizens will automatically be granted indefinite leave to remain”.
His government is now overseeing a scheme where EU nationals living in Britain have to a apply for leave to remain, and in around a third of cases the permission to stay is not indefinite.