It's pretty much an iron rule of political analysis that sudden shifts in public opinion attract huge attention, while anything approaching the resumption of normal service or simply regression to the mean generates relatively little comment. "Ukip surge" is a story; "Ukip goes off the boil" – which is what the Guardian's ICM poll suggests may be happening, with the party down six points – slightly less so. But the fact that Nigel Farage's smile may not be quite so broad today as it was back in May merits more than a passing mention.

Obviously, the fact that Tory support has been stuck at or below 30% since the beginning of the year, while at the same time support for Ukip – a party that only scored 3.1% at the election in 2010, remember – ballooned to around 16% (and even higher in some polls) deserved an explanation. So, too, did the election of 147 (up from just eight) Ukip councillors at the local elections. Clearly, something was going on.

But, whether we were inclined to put that something down to profound, populist disillusionment with politics as usual or instead pinned the blame on the Conservatives ramping up the rhetoric on Europe and immigration, maybe we were all just a little bit guilty of rushing to provide macro-explanations for what may well turn out to have been a micro-trend. It's a bit like blaming a heatwave on global warming – mixing up a change in the weather with the change in the climate. On that basis, Ukip's support could well turn out to be a temporary blip rather than a permanent shift.

Of course, it's easy to counsel Keep Calm and Carry On if you're not a sitting Tory MP or a candidate in a marginal constituency. If you are, then you're well aware that, at a general election, a few percentage points here or there translates into millions of votes nationally, which locally could mean the odd hundred or even thousand being cast for a 'kipper who can't win but can steal enough of your support to gift the seat to Labour or even the Lib Dems.

And even if you don't really buy the idea that the threat is as big as all that, or you're sitting pretty in a safe seat, you have – at least if you're a rightwing Eurosceptic politician or op-ed writer – something of a vested interest in talking it up. How else, short of calling for a potentially catastrophic vote of no confidence in David Cameron, do you put pressure on a prime minister who hasn't altogether given up on posing as a pragmatic liberal centrist, judging at least from his determination to protect spending on overseas aid, the NHS and pensioners, from his continued support for gay marriage, and from his recent defence of the UK's EU membership.

If you dress to the left, of course, you too might be prone to over-interpreting Ukip's now not-quite-so-inexorable rise. The latter, after all, neatly dramatises Labour's ongoing difficulty in connecting with both its core vote and with those whose support it requires in order to pick up some of the seats in the south and the West Midlands needed to give the party an overall majority – a difficulty that opinion research suggests has as much to do with cultural anxieties as economic credibility.

It feels terribly prosaic to put Ukip's rise down to a protest vote against the two main parties that has been growing since the 1970s but needs somewhere else to go now that the Lib Dems (and to some extent the nationalists, too) have themselves become one of the "above" in "none of the above". It's risky as well: the European parliament elections next year are almost bound to put the smile back on Farage's face, and it looks a fair bet that, this time, his party will not only top the 16.5% it achieved in 2009, but hold on to rather more of its support at the following general election than it managed in 2010, when it lost more than 80% of its vote-share from the year before.

That said, a little healthy scepticism never goes amiss. In 2015, if the coalition lasts that long, people will be deciding who governs, not sending a message. And they'll be voting under first-past-the-post and in much greater numbers, as well as in the light of Ukip councillors and MEPs probably making less of a difference than they hoped.

A month or so back, Farage was grinning like Lewis Carroll's Cheshire cat. No one's saying he's about to disappear – not soon, anyway. Still, there may well be less to him than many of us like to think.