Where the Brexit referendum campaign was won and lost

When David Cameron announced in early January that he would allow members of his cabinet to campaign on opposing sides in the EU referendum, the news was met with a shrug. Cameron had not yet renegotiated the terms of Britain's EU membership and was still maintaining the fiction that he might back a vote to leave.

Only one senior Conservative questioned the prime minister’s decision to suspend collective cabinet responsibility, veteran Europhile Ken Clarke.

“It’s most unfortunate that David is really now seeing the beginning of what is going to be a very difficult task for him to avoid splitting the party as he goes into this referendum campaign,” he said.

“He will have people who are openly challenging the policy of the government on the political future role of this country in the world.”

Six weeks later, Cameron was chairing the first Saturday cabinet meeting since the Falklands War, fresh from securing his renegotiation in Brussels. Six cabinet ministers told him they were joining the Leave campaign: Chris Grayling, Iain Duncan Smith, John Whittingdale, Theresa Villiers, Priti Patel and Michael Gove.

Of these, none was a surprise to the prime minister except Gove, a longstanding friend and political ally and a figure Cameron knew could add credibility to the case for Brexit.

But there was one Conservative heavyweight whose intentions were not yet known, London mayor Boris Johnson, one of the most popular politicians in the country and one who had never concealed his ambition to occupy 10 Downing Street.

Cameron had first promised an in-out referendum on the EU in a speech at Bloomberg’s London headquarters in 2013, a commitment he repeated in the Conservative manifesto before last year’s general election.

He made the promise as the United Kingdom Independence Party (Ukip) began snapping at the Tories' heels and pressure was building within the dominant, eurosceptic faction of the Conservative Party.

When Ukip won the biggest share of the vote at the 2014 European Parliament elections and two Conservative MPs defected to the party, it was clear to Cameron that to keep his party together, he could not afford to go back on his promise to hold a referendum.

At Bloomberg, he had spoken of far-reaching reforms of the EU itself and of Britain’s place within it but when he talked to other European leaders after last year’s general election victory, he began to understand the limits of what was available.

Angela Merkel told Cameron that Germany could not agree to his proposal for an "emergency brake" on immigration from the EU, which would have been in clear breach of the EU's freedom of movement principle. In Brussels, the British prime minister secured a deal that would allow him to curtail in-work welfare benefits to EU migrants for a limited period, along with other concessions including an opt-out for Britain from the principle of "ever closer union".

For Cameron’s EU partners, the deal was the maximum possible and there was a mood of self-congratulation in Brussels when it was agreed. Back in London, however, the media reaction was contemptuous, dismissing the renegotiation as meaningless and a betrayal of Cameron’s promise at Bloomberg of transformative change.

Johnson kept everyone, including the prime minister, guessing throughout the weekend before announcing his intention, even writing two versions of his weekly Telegraph column, one backing Remain, the other plumping for Leave. When he did reveal he was backing Leave, Johnson suggested that he would play a low-key role in the campaign, adding that he would not be taking part in “loads of bloomin’ TV debates against other members of my party”.

Cameron too had promised a respectful debate, with a minimum of “blue on blue” attacks among Conservatives but the day after Johnson’s announcement, the prime minister humiliated him in the House of Commons.

Poking fun at Johnson’s suggestion that a vote for Brexit could lead to a better deal for Britain inside the EU, Cameron added a dig at the London mayor’s leadership ambitions.

“I am not standing for re-election. I have no other agenda than what is best for our country,” the prime minister said.

The Remain campaign had a number of advantages from the beginning, with a single organisation called Britain Stronger in Europe uniting almost all those opposing Brexit. Leave campaigners were divided into two camps, the Ukip-dominated leave.eu and Vote Leave, led by Conservatives, which was to win the Electoral Commission's designation as the official pro-Brexit campaign.

Remain had the official support of all parties represented at Westminster apart from Ukip and the DUP, although a large minority of Conservative MPs and a handful of Labour MPs.

Perhaps the greatest advantage enjoyed by the Remain side, however, was that until the last few weeks of the campaign, when “purdah” came into effect, Cameron had the entire machinery of government at his disposal to make the case for staying in the EU.

At the beginning of March, the Foreign Office published an official government report saying that every alternative to EU membership would leave Britain “weaker, less safe, and worse off”.

The document analyses four main options, including agreements with the EU like those enjoyed by Norway and Switzerland and concludes that all would involve a loss of influence and the likelihood of higher tariffs for British exporters.

Foreign secretary Philip Hammond said the report was designed to "smoke out" the Leave campaigners, who had failed to clarify what future they advocated for Britain outside the EU.

During the opening weeks of the campaign, Vote Leave made a point of not endorsing any specific option for Britain’s relationship with the EU after Brexit, holding open the possibility of remaining inside the European Economic Area, like Norway.

A few weeks after the Foreign Office report, Duncan Smith resigned as Work and Pensions Secretary in protest against benefit cuts in George Osborne's budget. The former Conservative leader insisted that his resignation was not connected to the referendum but Ros Altman, a junior minister in his department, said she believed he had timed it to cause maximum damage to the party leadership.

“As far as I could tell, he appeared to spend much of the last few months plotting over Europe and against the leadership of the party and it seemed to me he had been planning to find a reason to resign for a long time,” she said.

Duncan Smith’s resignation marked a turning point in terms of the tone of the dispute within the Conservative Party, with Osborne becoming a marked man for the Eurosceptics.

A few days later, the terrorist bombings in Brussels brought the issue of national security to the centre of the campaign, with another former Tory leader, Michael Howard, claiming that remaining in the EU did nothing to keep Britain safer.

By early April, with some polls showing Brexit in the lead, there was a fresh controversy over a pro-Remain booklet delivered to every household in the country at a cost of £9 million in public funds. Cameron’s personal approval rating fell to its lowest level since 2013 in the wake of revelations in the Panama Papers about his family’s financial affairs.

The prime minister remained popular with Barack Obama, however, and the US president used a visit to London in mid-April to offer a full-throated endorsement of Britain remaining in the EU.

Obama’s warning that a post-Brexit Britain would be at “the back of the queue” in negotiating a bilateral trade deal with the US annoyed Leave campaigners, but it got the message across.

Meanwhile, Osborne was stepping up his campaign to frighten voters about the cost of leaving the EU, with an official Treasury report warning that the average household could lose £4,300 a year. The report infuriated the pro-Brexit camp and it was greeted with scepticism by many voters who were starting to get punch drunk from the pounding by Project Fear.

At the beginning of the campaign, Vote Leave was determined to avoid being too closely associated with Ukip’s anti-immigration message, calculating that immigration alone would not be enough to win the referendum. But towards the end of May, after more than a week focusing on immigration, Leave found its poll numbers improving.

At the beginning of June, Vote Leave produced a leaflet suggesting that Turkey was on the brink of joining the EU, with a map on the back highlighting the fact that the EU would then share a border with Iraq and Syria.

Turkey has no prospect of joining the EU in the foreseeable future but Vote Leave had found its most effective message so far to tap into popular disquiet about immigration.

By now, Labour canvassers were reporting strong support for Brexit among many of the party’s white working class supporters, with immigration the issue most frequently raised on the doorsteps. Immigrants were being blamed for pressure on schools, hospitals and other public services, as well as for the housing shortage and poor pay and work conditions. And many Labour voters appeared to have tuned out of a debate that was dominated by internal divisions within the Conservative Party.

At a Sky News referendum forum, Cameron faced hostile questions about immigration from an audience which was clearly unimpressed by his warnings of the economic cost of leaving the EU. As one international organisation and think tank after another outlined the risks of leaving, the public seemed to be switching off.

Some senior figures within the Remain campaign argued for a shift in strategy to make the positive case for EU membership but Osborne insisted on staying the course, convinced that the economic argument would ultimately prevail. There were signs in the polls of a modest shift back towards Leave before the murder of Labour MP Jo Cox on June 16th, an event which shocked the country and halted the campaign for three days.

When it resumed, the campaign was more muted and Leave campaigners feared that their momentum had been interrupted. A controversial Ukip poster depicting a crowd of refugees seemed discordant with the sombre mood after Cox’s murder and polls began to show a shift towards Remain.

Such a shift would have been in line with the expectation that voters drift back towards the status quo as an election approaches but last week, the polls began to tighten again. By the beginning of this week, both campaigns were nervous, with Remain anxious about the loss of Labour voters to Brexit and Leave fearful that voters would step back from choosing the riskier option.

By the time the polls opened on Thursday, pollsters, betting markets and the financial markets were all increasingly confident of a Remain victory. That confidence grew as the day progressed and when the polls closed, Remain campaigners were beaming while Farage and other Leave campaigners were resigned to defeat. It was not until the first results came in from Newcastle and Sunderland that the mood changed dramatically.