A relieved David Cameron hails the result, confirming he will be remaining as Prime Minister and leader of the Conservatives and claiming that the issue of Europe has now been dealt with. Despite this, anti-EU Tory backbenchers being to plan a coup and mount a leadership challenge, telling newspapers he has lost the confidence of the party.
A bloody political scrap ensues, which could result in Mr Cameron being deposed, a new leader appointed and another election held. If he hangs on, he will still need to get his renegotiation deal signed and sealed by Brussels so he can deliver on key reforms such as the “emergency brake” on EU migrant benefits.
Meanwhile, furious Brexiteers call for the vote to be re-run, with some claiming the campaign was an establishment stitch-up from start to finish. The British public’s evident enthusiasm for the Leave cause bolsters Ukip and the eurosceptic factions in other political parties, ensuring that the issue will remain high up the agenda for years to come.
The pound remains stable following the decision to maintain the status quo, while financial markets respond with relief. In the absence of any major financial shock, for most people in Britain life will continue as usual.
The triumphant Prime Minister thanks the British public for supporting him and promises to continue to hold Europe to account in an attempt to appease his defeated opponents. Seizing the initiative, he orders a reshuffle and gives key Cabinet posts to Brexiteers such as Boris Johnson, Chris Grayling and Liam Fox to unite his divided party.
However, if this charm offensive fails, Tory MPs may start opposing the Prime Minister and the Chancellor, George Osborne, in key Commons votes, triggering a leadership challenge and potentially another general election. If Mr Cameron wins the struggle, he will still face the obstacle of passing his EU reforms – but will be grateful that the economy has not taking a drubbing.
Meanwhile, Nigel Farage and Ukip continue to struggle for relevance and quietly fade into the background as it becomes clear that Britain is more pro-European than everyone assumed.
A stunned Mr Cameron makes a speech in front of Downing Street conceding defeat, probably announcing his intention to stand down as Tory leader in the autumn and allow someone else – most likely Mr Johnson or Michael Gove – to lead negotiations for a British EU exit in the meantime. His triumphant rivals give rousing victory speeches hailing the UK’s “independence day”.
Mr Cameron will immediately tell Brussels that he is activating Article 50 of the EU Treaties, the legal mechanism by which a member state leaves the bloc. From that day, the Government will have two years to negotiate a new relationship with the EU, working out things such as new trade deals, border security arrangements and the legal status of British expats. The negotiations are likely to be led by a senior pro-Brexit Cabinet minister.
Minutes after the result is announced, the pound takes a big hit on currency markets around the world, followed by share prices. The Bank of England may be forced to temporarily increase interest rates in response to the turmoil, leading to higher mortgage payments and borrowing costs for the public. George Osborne will attempt to calm things by stressing that negotiating a Brexit will take several years.
As the Tories deal with their own referendum fallout, all will not be well within the Labour Party either. Jeremy Corbyn’s low-key, unenthusiastic interventions and mixed messages on the campaign trail did not go down well with many of the party’s pro-EU MPs, so a Leave result may lead to fresh questions over his leadership.
If, as expected, Scotland has voted to Remain, Nicola Sturgeon says the country is determined not to be dragged out of Europe against its will. She demands a seat at the table during the exit negotiations, with the aim of securing the best possible deal for Scotland as she prepares to call another independence referendum.
As it become apparent he has been roundly defeated, a humiliated Prime Minister says he accepts the verdict of the British people and says he will stand down as Tory leader as soon as required. An immediate scramble to replace him ensues, with Boris Johnson the clear frontrunner. However, he may be challenged by Theresa May, who has stayed largely quiet during the referendum campaign.
Much as in the event of a narrow result, the value of the pound will dive as panic spreads in the markets, Article 50 will be triggered and a team appointed to oversee the Brexit. When the new Tory leader is elected, they could seek to capitalise on Mr Corbyn’s disorganised Labour Party and call a general election for the spring or autumn of 2017.
If Scotland also unexpectedly votes to Leave, Ms Sturgeon and the leaders of the other Scottish parties will be forced to accept the result. But the issue of Scottish independence will not be off the agenda, with the Scottish outcome likely to have been driven by disaffected SNP supporters who are as anti-Brussels as they are anti-Westminster.
Deep rifts have emerged within the Conservative Party as the campaign has unfolded, many of which are unlikely to be healed regardless of the result. The slim Tory majority at Westminster could be threatened as its MPs become increasingly rebellious, with Labour seeking to capitalise amidst the confusion.
With Mr Cameron definitely stepping down as leader ahead of the 2020 general election, popular Brexiteer figures such as Mr Johnson will seek to take his place, challenged by Theresa May and possibly Mr Osborne. The first item in the new leader’s in-tray will be to unite the party so it does not self-destruct before the UK goes to the polls again.