A supporter holds up a placard ahead of a speech by Leader of the UK Independence Party (UKIP) Nigel Farage, at the first public meeting in the partys referendum campaign as they kick off their 'Say No To The EU' tour in Margate on September 7, 2015. | JUSTIN TALLIS/AFP/Getty The Brexit debate: ‘Economic sovereignty’ vs ‘xenophobia’ Brexit campaigners struggle to find the right message for swing voters.

LONDON — Opposite the gothic grandeur of the Palace of Westminster stands a grotty brown high-rise building grandly named Westminster Tower. Inside this unassuming block, a campaign is germinating which has the potential to reshape British politics. It is on the seventh floor that the ‘Leave’ campaign for Britain’s impending referendum on European Union membership has quietly begun and strategists are already plotting how to fight any new deal David Cameron strikes with Brussels.

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While it is known that the referendum will be held before the end of 2017 — an election pledge Cameron would find it very hard to renege on — little else is known about the vote. The EU Referendum Bill is worming its way through the House of Commons and most believe the vote will be held next year. The bill does allow for an early vote, say in March 2016, but September is seen as the most credible option by campaigners. This would allow the prime minister time to nail down enough reforms to convince the British public that his renegotiation hasn’t been a total failure.

This uncertain timetable hasn’t stopped Brexit campaigners from planning. The Electoral Commission, which dictates how elections are conducted in Britain, will designate an official Remain and Leave campaign — most likely by the end of this year. Matthew Elliott and Dominic Cummings, two of the most experienced campaigners in British politics, are the most likely candidates to win the Leave designation. Elliott made his name importing Washington-style pressure groups to Westminster through the Taxpayers’ Alliance and Big Brother Watch, as well as leading the ‘No to AV’ campaign to victory in a referendum on changing Britain’s voting system.

Cummings also has a successful track record: he worked to stop Britain joining the Euro and ran the successful ‘No’ campaign in a referendum on Regional Assemblies — a new form of devolved government — in 2004. While Cummings has been working in government until recently, Elliott began laying the foundations for the Leave campaign with Business for Britain, a pressure group to give a voice to businesses sceptical of the EU. The aim of BfB is to fight for a better deal for British businesses; and if this can’t be achieved, it will recommend a Brexit. It is, in essence, an incubator for the No campaign until the time is right to go public.

Cummings and Elliott are focusing on a moderate message to convince voters to Leave. Their view is that the British people are generally Euroskeptic by nature and their campaign simply needs to assuage voters’ fears about life outside the EU.

"We are in a strong position," says Elliott. "UKIP [the UK Independence Party] can target the third of hard-core Euroskeptics who are motivated by the migration message, leaving the official Leave campaign to focus on the third of swing voters in the middle who are inclined to leave but have concerns about Britain's economic position outside the EU. Our polling shows these people need reassurance that life outside an unreformed EU would deliver greater prosperity and more jobs."

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But they are alone in fighting for a Brexit. UKIP was set up over two decades ago to get Britain out of the EU, and its current leader, Nigel Farage, was a major factor in forcing Cameron to hold a referendum. Farage is loathed and loved, a politician who has no time for moderation. He trades in dog-whistle politics that cuts through to a certain section of the electorate. This strategy put UKIP first in last year’s European elections and garnered 3.9 million votes at the general election. But the party has failed to crack Westminster and some Conservative Euroskeptics are concerned about the toxic effect he might have on the Brexit cause.

While the Elliott-Cummings group are waiting to see what Cameron turns up with — although the initial signs don’t strike them as promising — the UKIP leader is impatient to get shouting, not least because he has a good idea of what Cameron’s new deal will amount to.

Farage believes that Britain’s post-negotiation settlement will amount to some opt-outs on the Working Time Directive, relief on benefits for migrants and, most importantly, associate member status for the United Kingdom. This might sound wishy-washy but it would be sold to the electorate as a major change: a new category of EU membership created just for Blightly. Associate membership could be seen as the foundation of a two-tier Europe — something Conservatives have been hankering after for years — or a new badge for the status quo. Farage naturally sees it as the latter.

If his prediction proves to be true, associate membership may risk scrambling the whole debate as both sides project different ideas of what it means. UKIP believes the prime minister will have the upper hand in the campaign to Remain, and if he is not challenged on the associate membership early on, he will win the referendum by a landslide. The party has duly begun campaigning vigorously in case the Prime Minister returns with a deal soon. Farage hit the road in September as part of UKIP’s ‘Say No — Believe in Britain’ tour, which will encompass 300 pubic meetings before the year is out. Rallies and debates of all sizes will take place, powered by Farage’s unfiltered message about borders, migrants and his vision of Britain’s life outside the EU.

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There is yet another factor in the Eurosceptic mix: Arron Banks, a multimillionaire donor to UKIP. While the Cummings-Elliott campaign is operating below the radar for now, Banks’ ‘TheKnow’ operation is doing the opposite.

Its Facebook page has gathered over 125,000 likes and thousands of supporters have signed up. Sixty people are working on TheKnow campaign, as well as 50 more in a call center (in Britain, not Bangalore). Whereas the Leave campaign is focusing on jobs and economic stability, TheKnow has other ideas. "We believe that immigration and borders are the number one issue that the referendum will be fought on," says Banks. "We need an Out campaign that is more than very clever people talking about how very clever they are. It will be fought and won in towns across Britain, outside of the Westminster bubble."

The danger for the moderates in the Brexit camp is that the divergent messaging of UKIP and Banks could be used by the Remain campaign to paint those wanting to quit the EU as a dangerous, radical and possibly even xenophobic gang.

This is what happened during the 1975 referendum, when the British public were turned off voting ‘Out’ by the hard-left Labour MP Tony Benn and former Conservative minister Enoch Powell. If Labour’s Jeremy Corbyn — who is thought to be a Euroskeptic at heart — and UKIP’s Farage become the prominent Brexit voices this time, the British public would likely follow their natural instinct: to keep calm and carry on.

Sebastian Payne is deputy editor of the Spectator’s Coffee House blog.