Hard and fast.
It did no good. Their minds had been already made up. The Leave campaign's unending focus on immigration from the EU had overwhelmed all the opposing arguments from the Remain side. More precisely, the unrelenting focus on immigration post the 2005 accession of the A8 countries is what did for Remain. Most damaging by far was the Conservative promise to reduce immigration to the tens of thousands, an unachievable aim the leadership had never been serious about, and yet kept even after winning their majority in 2015. David Cameron's claims that his renegotiation, extracting concessions on benefits, would somehow bring the numbers down was specious and he knew it. Migrants from Europe came to work, not claim benefits.
Few politicians dared to make a positive case for the wave of migration from eastern Europe, instead either making false promises or pretending to listen to concerns while doing nothing. The coalition government went so far as to abolish the fund that had directed increased spending to areas of the country where migration was highest. That 5% of nurses and 10% of doctors working in the NHS were EU nationals made no difference; most chose to believe that immigration was in fact a drain on the health service, when the opposite was the case. Labour voices that had previously spoken up for migrants were drowned out by other MPs panicked by what their constituents were telling them. The last minute pledge to work to change the rules on freedom of movement came far too late to make any difference.
The Remain campaign had started out believing that a repeat of the "Project Fear" tactics seen in the independence referendum would work again two years later. What Remain had not reckoned on was the remarkable dishonesty of the Leave campaign: almost every single claim made was a lie, and yet it did them no harm. By far the most egregious was how many times over Leave spent the money they claimed would be saved by leaving the EU. It was variously promised to the NHS, to cut VAT, to keep up the payments the EU made to universities, farmers, the arts etc. The internet was meant to have made fact checking the claims of politicians all the easier, and still it made no difference. All politicians were liars, went the refrain, so why would anyone bother? The required neutrality of the broadcasters meant they had to treat the figures produced by Leave with credulity, even when they were fantastical. With the vast majority of the print media virulently anti-EU, producing front pages that day after day warned of a new migrant surge, any attempts to move the debate away from immigration on to the economy, how the UK wanted to be seen in the world and how it would affect the rest of Europe failed.
The morning of June the 24th was grey and wet, as much of the previous month had been. The exception were the images beaming out from every TV screen: the grinning, jubilant faces of Boris Johnson, Michael Gove and Nigel Farage. David Cameron, his face ashen, begrudgingly congratulated the Leave campaign at a dawn press conference in Downing Street, where he also announced his immediate resignation as both prime minister and leader of the Conservatives. Cameron in the past few days had tried and failed to come to terms with the extent of his failure, what he now recognised as his act of the utmost irresponsibility in promising a referendum. With the focus on winning the 2015 election, the Tory leadership had failed to recognise that its success would also be its downfall. The coalition it had put together to win that election, overwhelmingly focused on voters over 40, was massively opposed to the EU and resistant to change. The Tories had imagined that Labour voters would make up the difference. Instead, faced with a Tory government, continuing austerity and without the prospect of any apparent improvement in their lot, many decided that leaving couldn't possibly make things any worse.
George Osborne took over as interim prime minister, launching his bid to become party leader a year earlier than he had imagined would be the case. Osborne ended up finishing third, behind Michael Gove and the all conquering Boris Johnson. Johnson within days of taking over conspired behind the scenes with the SNP for a vote of no confidence to be called. While Labour opposed the vote, the other parties voted in favour, and a snap general election was called. Jeremy Corbyn campaigned valiantly on a manifesto designed around leaving the EU on the best possible terms, remaining in the single market, but the party was as divided as ever. The SNP swept the board in Scotland, Plaid Cymru and UKIP picked up seats in Wales while Labour fell back even further in England, the Tories under Johnson winning a landslide victory.
Writing from the vantage point of 2040, with Scotland long independent having rejoined the EU, Wales on the cusp of its own independence vote with the polls suggesting a clear majority in favour of seceding from England and Northern Ireland, and London an effective city state, with Neo Labour mayor Owen Jones entering his fourth term having negotiated a free trade agreement with the EU where the Tories had long refused to, it's easy to see how disastrous the Leave vote was. Johnson lasted only 2 years as prime minister before a scandal involving his giving the home address of a BBC journalist to a underworld figure forced his resignation. One of the first moves of his successor, Michael Gove, was to join in with President Trump's attack on Iran. The last British troops leave Tehran in September, with the total number of dead numbering over 5,000.
The Leave campaign never had a plan for what to do in the event that it won. While the worst predictions of Remain were not realised, at least not in the short term, the results over time have if anything been worse. With the Tories failing to agree a trade deal with the EU, everything reverted to WTO standards. With the advantages of being in a trade block gone, the global manufacturers who had based their operations in the UK one by one relocated to the continent. Communities that had already been hit hard by the 2008 crash were hit again, this time never to recover. The voters did however get their wish on immigration: with the UK no longer one of the fastest growing economies in Europe, net migration fell within 5 years to below the tens of thousands target. After ten years the pendulum had swung completely: more were emigrating than were arriving. Still however there is a comfortable majority for the Tories in England, Labour having split, merged with the Greens and Liberal Democrats in an attempt to create a progressive bloc, and then re-emerged as Neo Labour under the leadership of Will Straw.
The UK post-2016 seems to this writer the embodiment of H.L. Mencken's statement that "democracy is the theory that the common people know what they want, and deserve to get it good and hard". At least it would be if it didn't result in numerous Neo Labour MPs informing me of how these are very real concerns that we must listen to.