While the Labour leadership contest – and its gruesome fallout – will still dominate politics for weeks to come, the EU referendum is on its way back into the news. Until recently, I was confident that, barring a shock political event ahead of the vote, In would win. Now I’m much less sure.

There are two reasons for my doubts about the likelihood of an In victory.

The first is the instability of the In/Out polls.

That may seem a strange description of them. YouGov’s tracking poll shows what looks like a secular trend towards In, rather than instability (see below, up to May; recent polls show similar results). Over four years, Out’s lead over In has collapsed, despite the Eurozone and refugee crises. My hunch has been that this is down to people being confronted with the reality of a possible UK exit, which has forced more to engage seriously with the question for the first time.

So if there’s been a steady move towards In, why do I refer to instability? The reason is, we’ve still only had a few months of consistent leads for In. Go back just to December and the polls were tied. Go back a year further and Out had a comfortable lead in YouGov’s data. The longer-running Mori data shows Out has been ahead several times since the late ‘70s. Given these shifts, it seems to me too early to say we’ve seen an irreversible shift towards In (though it’s striking that support for In so far seems to have withstood the crises of the last few years).

It’s hard to dispute that views on the EU could well change at least as far as they have over the last eight months. Most people probably haven’t thought about the referendum much yet. As news and arguments develop, In’s lead may still prove to be assailable.

This brings me to my second reason why I’m not so confident of an In victory: opinion about the benefits and costs of EU membership look bad for the In camp. An Opinium poll this weekend showed that some of the underlying views of the EU point more towards Out than to In (I was involved in writing the poll, through my employers, DHA Communications).

Broadly, people think we’re worse off in the EU. On the economy, unemployment, crime and (unsurprisingly) immigration, more people think the UK would be better out of the EU than it is as a member.

This may be a huge problem for the In campaign. It’s generally expected that the campaign will focus on the risks and costs of a UK exit, since an emotional campaign counting on popular attachment to the EU is unlikely to resonate (and negative campaigns beat Scottish independence and AV). But at the moment it’s far from clear that many voters really believe that an exit would bring costs:

A similar question asked ahead of the Scottish Referendum reflects the challenge facing In supporters.

Before that referendum, ICM repeatedly tested whether independence was expected to be good or bad for Scotland’s economy. It consistently found a lead for ‘bad for the economy’: starting at 17pts (48/31) in the earliest poll, a year before the referendum (a parallel to the situation we have now, when most people haven’t thought much about the debate).

In this way, the EU In campaign seems to be starting from a weaker base than the anti-Scottish-independence campaign did. The overall In/Out EU polling currently looks very similar to how the Yes/No Scotland polling looked a year before the referendum: the status quo having a lead of roughly nine points. But No in Scotland could strengthen their support by drawing on the plurality-held belief that Scotland’s economy would suffer by leaving. The EU In campaign can’t yet do that: first it must persuade more people that there are economic costs to a UK exit worth worrying about.

One source of optimism for In from the Opinium/DHA numbers might be the higher proportion of people who think an EU exit wouldn’t make much difference. If that one in four could be persuaded that the UK would be worse off out, views on the consequences of a UK exit would become similar to the 2013 views on a Scottish exit from the UK. That said, there’s no clear reason why views should inevitably change in that direction, instead of even more people thinking the UK would be better off out.

I still think In is more likely to win than Out. The vast majority of polls since mid-2013 have shown In to be ahead, often comfortably so. But opinion seems to be changeable, and those who want the UK to leave the EU look so far to be winning in the very argument on which their opponents will depend.