After placing second in a by-election in Rotherham last Thursday, the United Kingdom Independence Party (UKIP) has vaunted to the center of British politics, with newsmakers wondering whether UKIP will, after two decades, finally emerge as a real force in British politics.

The by-election, which resulted after Denis MacShane, a Labour MP, resigned due to the ongoing expenses scandal (MacShane had submitted 19 invoices for reimbursement for non-covered expenses), should have been a non-event. One Labour MP was replaced by another Labour MP, Sarah Champion, who won over 46% of the vote, which was actually an improvement on Labour’s performance in the 2010 election, when MacShane won just 44.6%.

So why has the sleepy little constituency in South Yorkshire been treated like a political earthquake?

With 21.8% of the vote, UKIP’s second-place finish was its best-ever result in an election for the House of Commons.

UKIP was founded by Conservative Party rebels in 1993 in opposition to the Maastricht treaty (the European Union treaty that established the single currency).  Its primary characteristic as a party is its eurosceptic nature, but its ‘pro-British’ posture means that it has adopted harsher anti-immigration and anti-Muslim stances than any of the three major UK parties, notwithstanding a robust strain of euroscepticism within the governing Conservatives under prime minister David Cameron.

Cameron famously referred to UKIP as a bunch of ‘fruitcakes, loonies and closet racists’ in 2006 shortly after winning the Conservative leadership.  It was probably not far from the truth in 2006, and it’s probably not far from the truth today.  Despite the hand-wringing across England, UKIP is not necessarily any stronger or weaker than it already was before last week’s by-election — and winning about one-fifth of the total vote is hardly dominant. Part of its ‘success’ comes from controversy surrounding the local Labour-dominated council removing three children from foster parents, apparently on the basis that the foster parents were UKIP members.

Nigel Farage, UKIP’s leader (pictured above) declared after the by-election that UKIP is ascendant:

“We have established ourselves now as the third force in British politics. We have beaten the Lib Dems in all forms of elections over the course of this year. We are clearly and consistently now above the Lib Dems in the opinion polls.

“There is an upward trend. And I think the UKIP message is resonating with voters and not just Tory voters. There are plenty of voters, particularly in the north of England, coming to us from Labour and the Lib Dems.”

Farage, who’s known less for statecraft than for his stunts at the European Parliament (he’s been an MEP since 1999), would certainly like to think so.

But despite clear signs that UKIP would indeed make gains if the 2014 European elections and the 2015 general election were held today, UKIP is unlikely to become a truly powerful force in UK politics anytime soon.

Here are five reasons why.

By-elections are, by definition, one-off events skewed by odd factors.

By-elections in the United Kingdom, like special elections in the United States, have a tendency of emphasizing either unique local issues or otherwise focusing on timely national issues in a unique way.  It’s also important to remember that Labour’s hold on the Rotherham constituency was never in doubt, and UKIP’s result was so strong because neither the Tories nor the Liberal Democrats have ever really had a chance to win in Rotherham — in 2010, the Conservatives won just 16.7% and 16.0%.  UKIP, by the way, won 5.9% in that election — the by-election result was a solid 15% swing, but it’s important to realize it wasn’t starting from zero.

UK voters are increasingly disillusioned with Labour and the Tories, but with the Liberal Democrats in government, there’s no third party currently available to them.

Increasingly, UK voters have turned to the Liberal Democrats, to register disapproval with both Conservatives and Labour.  The predecessor of the Liberal Democrats, an alliance between the old Liberal Party and the Social Democratic Party (founded in 1981 by Labour moderates), became a strong alternative in the 1980s for voters opposed to both a leftist Labour party stuck in its trade union roots and Margaret Thatcher’s stridently free-market Tory government.  With Labour (and more quietly, the Tories) supporting George W. Bush’s military action in Iraq, anti-war voters turned to the Lib Dems again in record number in the 2000s.  Steadily, the Liberal Democrats have gone from 17.8% of voter support in 1992 to 23.0% in 2010, tripling their representation in the House of Commons and, since 2010, they have served in government in coalition with Cameron’s Tories.

But since the 1992 election, the combined share of the vote for both the Conservatives and Labour has decreased in each election from just 76.3% in 1992 to 65.1% in 2010.  That reflects more than just Lib Dem support.  UKIP itself has seen its support increase in each election — a paltry 0.3% in 1997 grew to 1.3% in 2001, to 2.2% in 2005 and finally 3.1% in 2010.

Yet the stridently nationalist and overtly racist British National Party’s support is also on the rise — up to a high of 1.9% in 2010.  But the relatively small shares that each of UKIP and the BNP attract are ultimately more important than their marginal gains.  So while UKIP and the BNP have both been making progress for the past 15 years, it’s been glacial at best.

In the next general election, currently scheduled for 2015, it seems perfectly plausible that voters looking for an alternative to both the Tories and Labour could end up supporting UKIP, and pundits in Britain’s right-wing dailies seem to divide on whether they believe UKIP can (or cannot) poach seats from the Tories by getting to the right of Cameron’s government.  But if the Lib Dems, with a much wider appeal to UK voters on both the left and right, leave government for the opposition benches, it seems farfetched to think that UKIP could turn a one-time bonanza into a permanent realignment.

Parties like UKIP, historically, have never garnered true power through elections in Western Europe.

In France, despite winning almost one out of every five votes for president in the first round of the presidential election earlier this year, Marine Le Pen’s stridently nationalist Front national (National Front) won just two seats out of 577 in the parliamentary elections in June 2012.  You can say the same thing about many of the nationalist, right-wing, anti-Muslim, anti-immigration parties throughout Europe.

Of course, in some Western European countries with proportional representation, ultranationalist parties have won greater numbers of seats — Geert Wilders and the Partij voor de Vrijheid in the 2010 Dutch election (Party for Freedom), Pim Fortuyn’s personal list in the 2002 Dutch election and Jörg Haider and the Freiheitliche Partei Österreichs (Austrian Freedom Party) in the 1999 Austrian election come to mind.  But though Haider briefly joined the Austrian government for three years, and Wilders provided outside support to the Dutch government from 2010 until earlier this year, such electoral success has traditionally been short-lived.

UKIP has been a factor in European elections for a decade.

In the 2009 European elections, UKIP won more support than any party except for the Tories — with 16.5% of the vote, it outpolled Labour and the Liberal Democrats and won 13 seats.  It won 12 seats and 16.1% of the vote back in 2004 (besting the Lib Dems in that year), and it won even a handful of seats and 7% support even back in 1999.

So there’s every reason to believe that UKIP will do well in the upcoming 2014 European elections, but that would have been the case regardless of the Rotherham result.

By and large, alternative British parties do incredibly well in European elections, partly because they are conducted with a form of proportional representation and partly because it’s an opportunity for UK voters to make a protest vote in a forum that has much less effect on everyday life than a vote for the House of Commons.  So, for example, in 2009, even the UK Green Party, truly a non-factor in general elections, managed to win 8.1% of the vote and two MEPs, and even the BNP won 6.2% and two MEPs.  Given that UKIP is so wholly associated with its anti-Europe identity, you would expect it to thrive in elections where the UK’s role in the EU is routinely the most important campaign issue.

Scotland is still a member of the United Kingdom and there’s no English parliament.

In the 2010 general election, the Tories won 39.6% of the vote solely within England — about 3.5% better than within the United Kingdom generally.  UKIP won 3.5% of the English-only vote and the BNP won 2.1%, with Labour performing marginally more poorly and the Lib Dems marginally better within England. That lines up with longstanding historical data that show England is more conservative (or at least less anti-Tory than in Scotland) than the rest of the United Kingdom.

There’s reason to believe that UKIP, along with the Conservatives and the BNP, could gain if Scotland achieves full independence, leaving the United Kingdom comprised of just England, Northern Ireland and Wales.  There’s also reason to believe that, were England to attain its own regional parliament (like Scotland, Wales and Northern Ireland have each obtained through the ‘devolution’ policies of Tony Blair’s government), UKIP might gain.

For now, though, Scotland still comprises around 8.5% of the UK’s population, and England has no regional parliament, so neither is at present a realistic option for Farage.