Last July, Lord Ashcroft Polls held an unusual event called Immigration on Trial, reported on by my colleague, Peter Hoskin.

It was a mega-focus group, exploring people’s reactions to different arguments about immigration.

Last week, I attended the second such event – Europe on Trial – which followed a similar format. Eighty people with a wide range of views on the EU were brought together to discuss the biggest issue facing the nation, and to hear various expert opinions on the topic.

It’s worth at this stage giving an explanation – and a defence – of focus groups as a means of market research. They’re much-maligned, particularly because they’re often misused by political parties.

A focus group is not – I repeat, not – a way to find out what the public think. That’s a quantitative exercise, which is far better done through opinion polling. A focus group is used, instead, to do the qualitative work – to test different messages, for example, and particularly to find out which arguments are most effective at changing people’s minds.

As Lord Ashcroft himself said at the start of the event,

“While a poll can tell us how many people think one thing and how many think another, discussions like this help to reveal why people think as they do.”

Knowing what people think is useful, but knowing how to change what they think is the essence of political campaigning.

A focus group can never lead you, and it should never supplant your beliefs, but done properly it can help to sharpen your arguments.

Just as Lord Ashcroft’s polling uses larger samples than most ordinary polls, so last week’s event was on a much bigger scale than is usual. I’ve observed and led focus groups with eight or nine people, but eighty gave a completely different dynamic.

Most notably, it allowed for much greater representation of the full scale of opinion. As we know, relatively few people are fully signed up europhiles or Better Off Out enthusiasts – the bulk of the population still sits along a scale stretching from one position to the other. In the inevitable in/out referendum, swaying those in between will be key to victory or defeat, which made the event particularly fascinating.

The results of the current round of research will be published in a few weeks, so as an observer I won’t be pre-empting those conclusions now. But what I can discuss are the broad implications for how the eventual referendum campaign should be fought.

Politics has an internal tension at its heart.

Those of us who work or volunteer in the ranks of one side or another are by definition pretty certain about our views. We write blogs, knock on doors or dish out leaflets because we know what we believe and we want those beliefs to win out.

By contrast, those who actually decide elections and referendums are completely different – floating voters who are unsure and thus open to persuasion by either side.

To win, the former group have to gain an accurate insight into minds that are almost unimaginably different from their own.

In that sense, the political process is the unshakeable in pursuit of the undecided.

It’s a unique problem, which plenty of political campaigns have failed to overcome. The few true believers in AV simply could not understand how the electorate didn’t share their enthusiasm for a new voting system. CND protesters never got their heads round the majority view that the Bomb was a preferable option to domination from Moscow.

The challenge is further complicated by the fact that the British electorate are the most politically savvy in the world. The Blair experience in particular educated the nation in political sharp practice, instilled a deep scepticism of messages flowing from Westminster and helped to create a culture which is quick to sniff out inconsistency or hypocrisy. As I warned recently, voters are already starting to weigh up anti-EU arguments through the spectrum of the Scottish referendum debate – campaigners can’t relax on the basis that the EU referendum is still years down the line.

This is why events like last week’s are crucial to the outcome of the in/out referendum on the EU.

Convinced eurosceptics know all about the Brussels institutions, the vetoes, Qualified Majority Voting and the Maastricht Treaty, which are important to give a philosophical underpinning to the position, but we must also recognise that all those things do not matter a damn in convincing the rest of the electorate to vote Out. Just as importantly, we need to remember that the arguments which appeal to our base are not the same thing as arguments which will actually win the referendum.

Indeed, arguments which appeal to those who already agree with you may even deter those you need to win over.

When I and my then colleagues at The Freedom Association launched the Better Off Out campaign, eight years ago, it was specifically intended to make the eurosceptic case relevant to the wider electorate. That’s why we chose the name – on the basis that undecided voters are more driven by the prospects for the economy, for their own job and for those they care about than in the technicalities with which the eurosceptic movement is all too often obsessed.

Europe on Trial will no doubt provide insights into which arguments work, and which don’t, for the pro-EU and anti-EU sides of the debate alike. We should pay close attention and learn from them – you can be sure that the other side will do so.