The rise of the unpopular populists.
To give the typical nerdy fuller answer, the rise is in some way attributable to all these reasons, but also a couple of others. Unlike much of the rest of Europe, we haven't seen a rise in support for the traditional far-right, somewhat to do with how the BNP have turned into a basket case and the EDL are a bunch of thugs led by a convicted violent criminal with an identity crisis, leaving those who are racist and xenophobic (decreasing numbers, it should be stressed) with having to compromise their feelings somewhat.
Far more important is that the media and indeed most politicians have given Farage almost a completely free ride. Farage has appeared on Question Time more often than any politician other than Vince Cable, regardless of the amount of support his party was up until around this time last year attracting. When interviewed one to one, which is rare, he's also barely questioned on his party's policies beyond getting out of the European Union, which when even so much as glanced at fall apart. A 40% increase in the defence budget, doubling the number of prison places, and spending £90bn building new nuclear plants? You can make the case for those policies individually perhaps, but all at the same time? Pull the other one.
Farage and UKIP have been most obviously helped through the completely wretched scaremongering that has surrounded the upcoming lifting of the controls on the number of Bulgarians and Romanians who can come here to work. This hasn't just been thanks to the usual suspects at the Mail and Express, although they were in the vanguard, but also to politicians who either haven't bothered to challenge such silliness or have in fact connived in it. One of the most basic lessons of politics is that you don't win by stealing the policies of outlier parties, as the Eastleigh by-election ought to have shown.
By doing so, you either buy completely into their myths, or give them further credence: witness Sajid Javid on QT last week talking almost solely about making Britain "a less attractive place" for Bulgarians and Romanians to come to, when there is no evidence whatsoever that the level of benefits plays a significant role when people make decisions about where to go, or indeed when all the evidence suggests recent immigrants overwhelmingly put more in than they take out. It's a measure of just how far the debate has been shifted when Farage isn't called out on his linking of Romanians to crime; it may be just about true that 30,000 people giving their nationality as Romanian have been arrested in the past 5 years out of a population in the region of 100,000 (it's not clear whether these arrests were all made in London or not), but this is close to being a worthless statistic when it's convictions that matter, not arrests. We also quite rightly worry when black and Asian men are disproportionately stopped and searched, but not it seems when it's foreigners linked to criminality by politicians.
Another factor is that once a bandwagon's going, plenty of people jump on precisely because it's seen to be the thing to do. Some of those who've voted UKIP in recent by-elections would no doubt be aghast at the views of Godfrey Bloom, and wouldn't dream of supporting a party where he's one of the most senior figures, but as a protest at the way politics has been conducted in recent years it makes sense to climb aboard.
It is therefore just a little rich when UKIP complains that its poorly vetted candidates for the local elections on Thursday are being, err, held up to the same standards as everyone else. You can of course quite easily portray most people who have a presence online as being unpleasant or worse by cherry-picking questionable tweets or posts and presenting them out of context, yet if UKIP wants to be considered the third or fourth force in politics in this country then it can hardly expect to be given the benefit of the doubt, as it has been up to now.
The question of how you respond to UKIP's rise is a far more difficult one. Difficult as it is to disagree with Ken Clarke when he reprises David Cameron's old line about the party being made up of closet racists and other assorted eccentrics, just dismissing Farage out of hand is a dangerous game. Lord Ashcroft's polling may well have suggested that a large percentage of UKIP's support comes from those who are irreconcilable, and as likely as it is that come 2015 the vast majority of those currently flirting with the party will return to one of the main three, a UKIP victory in next year's European elections isn't something to savour.
The very first thing to do then has to be stop agreeing with them: we are not going to be flooded by Romanians and Bulgarians come January, nor will those few who do come have any discernible impact on the number of jobs available for our own young people.
Second, challenge them on their policies which have nothing to do with the EU (PDF): what's their stance on the NHS? Why do we need to double the number of prison places when crime is at a historic low? Why do we need to increase the defence budget so massively if we're going to leave peacekeeping and interventions to others, especially when we face no conventional threats whatsoever? How can their proposed flat tax possibly be fair, or affordable? How can they reconcile their opposition to gay marriage or decriminalising drugs with their claim to be a libertarian party? What impact will a halt to immigration have on the economy?
Third, question their every assertion on the EU, whether it be how much it costs through to their claims on red tape and the amount of laws decided in the European parliament. Hit back at their every soundbite or statistic with one that either flat out contradicts it or disputes it.
And fourth, just wait. UKIP and Farage are still at the moment a media novelty, and one that will be quickly tired of. They will only become a true fourth force in politics if they are indulged as such, as their overall appeal to the majority as anything other than a convenient protest is slight. Populists who fail to make a true political breakthrough quickly fade away. Farage isn't close to being a Boris Johnson yet.