It’s almost Easter, so it is also time for the Political Studies Association annual conference, held this year in Manchester. I had the great pleasure of sitting on a roundtable on UKIP with Rick Whitaker, Phil Lynch and Matt Goodwin, where we discussed the party’s support, strategy and organisation: much debate ensued. We’re producing a series of blog posts on our contributions, but out of the roundtable, another idea emerged for me that I would like to explore here.

The central idea is simply that UKIP might be about to reach a point where its current upward trajectory comes to an abrupt end.

Let’s consider where the party finds itself presently.

The European elections next month appear to be locked in for UKIP: the broad expectation is that they will come first (either in vote share or seats won). Indeed, there’s probably more downside risk than upside here – there would be more media interest in failing to come first than in coming first, and the marginal benefits of gaining extra seats seems very small. The likely difficulty of building a group will also be a source of discomfort.

However, the party’s focus has shifted towards Westminster and the 2015 general election. This is partly just because of lack of scope for getting more out of the EP arena and because as the party has broadened its focus as a more generic protest party, the more it sees opportunities to gain a foothold in the House of Commons. Witness Nigel Farage’s claim that he will stand down immediately if the party doesn’t win a seat next May.

Thus, it is 2015 that is vital to UKIP’s continued success. That either means a seat, or it means influencing the other parties to adopt their positions.

Despite the growth in local organisation, and the advance in the polls, it still seems unlikely that UKIP can take a seat in the general election. The party still lacks a positive agenda – its policies are all about what it dislikes – which put a ceiling on how far it can take the disaffection that Matt (and co-author Rob Ford) has identified as the wellspring of UKIP support.

But the scope for affecting other parties is also closing in. The Tories have probably moved as far as they will in promising the renegotiate-and-vote scenario laid out last year. The LibDems appear to be doubling-down on a pro-EU stance, at least for this electoral cycle. And Labour have largely resisted any pressure to commit to a referendum, despite Miliband’s speech last month, which was in any case very conditional. Assuming that Labour will be the other big winners in May (as the party of opposition), then that is not likely to change very much.

Thus the outcome of the 2015 general election becomes vital.

Anything other than a Conservative majority means that a referendum on EU membership will not take place before 2020. The aggregate data shows a narrowing of Labour’s lead over the Tories during the past year, which suggests that we might be heading for another hung Parliament (especially if the UKIP vote holds up, offsetting LibDems losses).

Even if the Tories do win a single-party majority, then any in/out referendum will not necessarily benefit UKIP as a party, since a role as the leaders of the ‘no’ campaign would be highly contested, given their poor relations with other parties and with large sections of the wider anti-EU movement in the UK. The process might end up highlighting their marginality, rather than their centrality.

All of which potentially leaves UKIP in a very difficult position.

Let’s consider a situation in May 2015, where Cameron just holds on to the largest number of seats and enters another coalition. By definition, this will be with parties that are more pro-EU than the Conservatives, so a referendum might well get shelved (or turned into the Labour version). UKIP, without a seat in the Commons, then loses Farage as he follows through on his promise. Recall that he’s stepped down as leader before, in 2009, to fight John Bercow in the general election. Farage is a leader, rather than a manager, and has never evinced great interest in the daily grind of running a political party.

UKIP then faces an extended period where it will lack opportunities to push its agenda. Labour will be largely shielded from pressure, either from a post-election honeymoon (if it wins) or as an opposition party that can snipe at the government. The Tories will either be constrained in a coalition, or will be locked in an internal power-play for a new leadership. That latter option might serve UKIP’s agenda, but let us recall that the last time the Tories went for a big play on Europe – in 2001 – that did them no favours electorally, which is always the prime interest of the party.

At a European level, treaty reform still looks to be a way off, as the eurozone crisis eases. In addition, the election of a British government that wasn’t pushing for renegotiation would also remove some of the current interest in the subject, working on the ‘let sleeping dogs lie’ model. Without any impending enlargement or removal of free movement restrictions during the period to 2020, that source of pressure on immigration politics would also be tighter than before.

UKIP would itself be trying to find a new leader who held the media’s attention in the way that Farage does, and would probably fail. Despite the huge growth in membership, the party still lacks depth of strong political figures, especially in terms of external profile. Paul Nuttall and Diane James would be the most likely choices, but neither possess Farage’s teflon characteristics or ability to tap into popular politics.

At best, UKIP could find itself spending five years fighting by-elections and recycling the same message it currently does, but without its best asset in play. That suggests that diminishing returns might be the leitmotif from 2015.

In turn, this suggests three possible futures for the party.

The first is a return to Farage, in an effort to keep the party knocking at the door. It wouldn’t surprise too many people if he stayed on next year, if he felt the opportunities were still there, and his ability to shape the party would remain very strong.

The second is a progressive withering of a party that loses its way during the next Parliament. A weak(er) leadership, a lack of opportunities, progressive co-option of policy and personnel by other parties; all would contribute to a slow decline to a rump membership that looks much like the original UKIP of the 1990s.

The third option is the most intriguing (for me, at least). In this, an initial loss of direction after 2015 would leave the party open to being taken over by a new, charismatic leader, who would effectively reinvent the party. As one colleague (Aurelien Mondon) listening at the PSA roundtable noted afterwards, this is what happened with the Front National in France with Marine Le Pen’s leadership.

That could mean the creation of a more positively-framed agenda, with a more coherent package of policies that fitted a conventional mold. By extension, that would mean losing some supporters who had been able to live within the ambiguities of current UKIP policy, but would also bind in remaining members more closely. The logical direction this ‘new UKIP’ would take would be a populist one and would potentially mark a key change in the British political system.

Whether any of these scenarios comes to pass will only become clear in the fullness of time, but whatever happens 2015 will be a vital year for UKIP.