Though tempting on recent experience, it would be reckless to assume that nothing of any lasting significance will happen at this autumn's three main party conferences, which begin with the Liberal Democrats this weekend. But it may be a pardonable exaggeration to say that the most influential event of the season could be done and dusted before Nick Clegg and his party even get down to business on Saturday.

The annual conference of Britain's fourth party is unlikely to get more than passing attention when it gathers in Birmingham tomorrow for two days. But the UK Independence party, now to be officially renamed simply Ukip, is no longer merely a marginal player in the British party battle. If the cards fall Ukip's way over the next two years – and they well may – the party will significantly shape both the 2015 election and the politics of Britain and Europe in the generation to come.

Wednesday's latest YouGov poll for the Sun shows clearly why Ukip can no longer be dismissed as a joke. That poll had Labour on 43%, the Conservatives on 34%, and both the Lib Dems and Ukip trailing on 8%. That 8% is grim pre-conference news for the Lib Dems, of course. But it is brilliant news for Ukip. It says that they're up there, that they're in the game, that they matter. And they do.

Talk to Ukip's leader Nigel Farage, as the Guardian does today, and it is clear that he thinks the 8% rating sells Ukip short. Like most polling companies, YouGov does not mention Ukip when questioners prompt voters with the names of the main parties while polls are being conducted. Ukip support is thus buried within "Others", Farage argues. And he surely has a point. One company, Survation, does mention Ukip along with the bigger parties – and in its August poll, Ukip emerged on 12%, two points ahead of the Lib Dems.

Ukip support, classic protest voting much of the time, is clearly volatile. But it is on the up right now for some fairly obvious and potent reasons. One of these is clearly the eurozone crisis, which plays to a party that won't touch either the euro or the European Union with a barge pole – though Farage, who thinks it dated, now wants to abandon the party's pound sign logo. Another is the midterm unpopularity of the Tories, traditionally the well from which Ukip mostly draws its support. Neither of these reasons is going to disappear quickly, especially the eurozone crisis.

And this spike in the polls may be coming at the right time in the cycle for Ukip. The party was early into the field in Corby, where an emblematic swing seat byelection looms after Louise Mensch's resignation. Ukip won't win in Corby but it will almost certainly beat the Lib Dems, and they may press the Tories hard, perhaps even grabbing second place behind Labour. Then there are November's police and crime commissioner elections, where the party hopes to compete in the majority of contests and may spring some surprises on the expected low turnout of less than 20%.

These are all stepping stones towards the contest on which Farage's party is most focused. A year and a half from now, in the 2014 European parliament elections, Ukip aims to exceed its spectacular 2009 result, when it took 16.5% of the national total, claimed 2.5m votes, forced Labour into third place and won 13 seats. The prize for Ukip in 2014 is even bigger – to finish top of the poll, to force the Conservatives, first in 2009, into second or third place, and to increase the pressure on Tory MPs to commit to Farage's holy grail: an in-out referendum on Britain's membership of the EU.

It is no secret that many good judges at Westminster think that this is anything but a fantasy scenario. Most Tories to whom I have spoken in recent months believe both that Ukip will triumph in 2014 and that there is almost nothing the Conservatives will be able to do to prevent it. Many of the most passionately anti-EU Tories obviously say this for their own reasons. But the fatalism about Ukip's success goes much wider. Cooler and smarter judges like Lord Ashcroft are sceptical about the importance of the Ukip factor. But in general the Tories are spooked by it.

All of this matters, and it will matter a lot more as the 2015 election comes over the horizon. There are two main reasons why this is so. The first is the Ukip factor itself. From 2009's 16.5% in the Europeans, Ukip slumped to 3.1% in the 2010 general election. A disastrous fall? Undoubtedly. The party crumpled.

But that 3.1% – still nearly a million votes – may have made some of the difference between a hung parliament and an outright Tory win. Small though it was, the Ukip vote exceeded the majority in 21 marginals the Tories failed to win in 2010, including Ed Balls's seat in West Yorkshire. If Ukip does as so many expect, and fares even better in the 2014 Europeans than in 2009, the Tory fear of a palpable Ukip effect in the 2015 general election will be even greater than before, even if Ukip's vote tanks again as it did in 2010. Any Conservative with a majority of 1,500 votes or fewer may be at risk.

The second reason why Ukip success matters is because of Britain's place in post-eurozone crisis Europe. The competition between the parties on whether to promise an EU referendum – and, crucially, what question it would ask – is already intense behind the scenes. Every Ukip success is likely to push that competition further towards an in-out referendum pledge. Even if that does not come about – and a referendum on a less cut-and-dried choice of the sort that is apparently preferred by David Cameron would certainly cause problems for Ukip – the momentum of the whole process is towards increased UK marginalisation within whatever remains of the EU.

It may seem odd, when you look at Ukip's Birmingham agenda this week, to treat this party as one of the big movers and shakers in British politics. After all, nothing that will happen in the Ukip conference itself will move or shake the nation. But Ukip is a force to reckon with now, all the same. It is not an exaggeration to say the national destiny is at stake. And if Boris Johnson were ever to try to break the mould of British politics by launching his own party – what Farage described this week as an SDP moment on the centre-right – then who knows where the road from Birmingham may eventually lead?