First, the British people are worried about a particular sort of immigrant—those that they see as "foreign". This is a loose term, but essentially includes people who don't speak English—almost nobody that I have spoken to has any problem with New Zealand, Australian or US immigrants, for instance.
UKIP can pledge to target the immigrants that people fear because their policy is to leave the EU: the Tories cannot do the same because, even with the promise of the referendum—which will only happen if the Tories are re-elected with a majority and if Mars is in the House of Ares when a pig flies across the Thames in a dirigible, or something—their stated position is that they think we should stay in.
Second, UKIP believe that lower taxes will bring higher growth—not surprising when you consider that their fiscal policy was largely written by Tim Worstall (with contributions from other libertarian/minarchist bloggers). The Coalition is shifting the burden of tax away from the poor (good) but not actually changing the total tax take (bad).
UKIP also have a credible energy policy (again, much of it originally drafted by libertarian/minarchist bloggers (hem hem)): whilst most people may not realise that we are in severe danger of rolling power cuts next year, they do understand that their energy bills have soared. UKIP have a credible answer for this—the government should stop artificially forcing up energy prices.
Unfortunately, much of the legislation doing so comes from the EU (although successive governments of the last 20 years have added their own price-raising policies too—Osbourne's carbon floor price, for instance, is utterly, industry-fuckingly insane).
There are quite a few other differences too; however, one of them is that people can see themselves having a drink and a bit of a giggle with Nigel Farage.
And that's not simply because he likes to be interviewed in pubs; it is because he comes across as a guy who enjoys himself, and who genuinely thinks that the people of Britain should, in the end, also enjoy themselves.
This philosophy is miles away from the pinch-faced, high-voiced, bigoted, boring, public-health fascists and shrieking snobs of the Islington set—of which Cameron is perceived to be a member (alongside most other politicians).
UPDATE: it seems that Marina Hyde also agrees with this last point.
Farage wears pretty much everything lightly, from blazers to budgetary black holes. And this, one can't help feeling, is his deadliest weapon. He does possess a genuine political superpower: the ability to make it look as though his critics are taking things far too seriously.Yup. I've had a good few pints (and a fag or two) with Farage, and he's highly entertaining. Furthermore, he always stands his round...