If David Cameron had been watching Ukip's spring conference on the Skegness seafront, the critic who would most have spoiled his day was not Roger Helmer MEP, the serial rebel who celebrated his weekend defection from the Tories by calling the prime minister a "complete sell-out" over Europe.

Nor was it veteran Ukip MEP Godfrey Bloom, who later dismissed him as "an appallingly vacuous, pigeon-chested young man".

Helmer is 68, Bloom is 62, and they have been insulting the Tory leadership from the fleshpots of Strasbourg for years. They delight the equally elderly members of the UK Independence party, Britain's version of America's disaffected Tea Party. Stubborn, nostalgic and cheerfully insular, they are also very cross.

No, the new Tory defector whose scornful tone might have rattled Cameron was Alexandra Swann.

Smartly dressed and well-spoken, sporting long blonde hair and 3in heels, she does not fit the Ukip stereotype. No blazer and regimental tie, no beard or beer gut, Swann is researching a PhD on 19th century social Darwinism and the small state. She is also 23, a political anorak since 16, former deputy chairman of the Tory youth wing and a visible blogosphere presence.

As sunshine finally burned off overnight fog on nearby Skegness beach, Swann was cheered by 400 Ukip activists in the Embassy theatre for her assessment that Cameron's "Lib Dem-led business-hating coalition" – obsessed with Europe and windfarms – is already on the ropes.

So many people at the SW Surrey Conservative club (her tax-hating father is a member) feel betrayed by Cameron ("as true a Conservative as Belgium is a real country") that they will soon be following her into Ukip, she assured them.

All parties love defectors, the lifeblood of political hope.

But Ukip leader Nigel Farage MEP ("the first politician to be given the freedom of the City of London"), believes this time is different.

Given a rock star's welcome in Skeg on Saturday, he combined mockery of familiar Brussels targets such as EU president Herman van Rompuy with a renewed effort to broaden Ukip's appeal as the "commonsense" party of liberty within the democratic nation state.

"We want to be good Europeans, but we don't want to be run by people like [José Manuel] Barroso or Van Rompuy. We want a Europe of nation states," he said, where small employers and the self-employed, "heroes" ground down by bureaucracy, can smoke in their own pub or go fox-hunting if they want, he explained.

More and more young libertarians like Swann share his view, say party officials. The Guardian encounters an earnest 15-year-old who has made the journey from London and is on message: "The other parties are all the same. Only Ukip can save us."

Like most party conferences, Ukip's looks more middle class and middle-aged than young, though there is plenty of talk of restoring grammar school opportunities for the working class ("To get my kids the education I got I had to pay," says newspaper columnist Jon Gaunt) and a top tier of distinctly posh. It includes peers and academics such as economist Tim ("leave the EU and join the world") Congdon and educationalist Sir Chris Woodhead. He praises Ukip as the only party with "conviction, common sense and courage".

It is two years since the eurozone crisis first vindicated some of Ukip's predictions, almost two years after Cameron's failure to win a Commons majority forced the Tories into coalition with the pro-euro Liberal Democrats.

It is nearly three years since Ukip beat Brown-led Labour into third place in the 2009 European elections. With Labour worth barely a rude mention on Saturday, Ukip's leadership thinks its breakthrough into Westminster politics may be at hand.

That may be a tall order. In the 2010 general election Ukip got 919,417 votes to the Tories' 10,703,654, 8,606,517 for Labour, 6,836,248 for the Lib Dems – and 564,321 for the BNP, which Ukip dismisses as a leftwing party of extremists, so unlike itself.

Ukip may have 12 MEPS but it has no MPs. At local level it boasts just 139 councillors, mostly in parishes, 21 at district level and – in Cambridgeshire county, Huntingdon district and Ramsey parish councillor, the highly articulate Peter Reeve – all three.

Ramsey got international media attention when the controlling Ukip group decided to save money by cleaning the parish loos themselves – typical of its hand-on, localist worldview, says Reeve.

How can Britain afford to pay Europe £50m a day, send aid to nuclear India and waste money on bureaucracy when it cuts buses and care for the elderly, leaving potholes in the roads, he asks. Loud applause. Skegness's famous skipping mascot, the whiskery Jolly Fisherman, is deployed on conference literature and looks the Ukip type – jolly in a saloon bar way, but cross about quite a lot.

The party's strength is in small towns and rural communities, its attraction in Lincolnshire enhanced by hostility to migrant farm workers.

Chris Pain, Ukip's local candidate in 2010, tells the conference the workers undercut local wages, wire most of their pay home to Poland on Fridays and avoid UK taxes. More applause.

The populist politics of grievance are not confined to Ukip, which shares with bigger parties a desire to cut taxes and the state while proposing all sorts of costly plans – like more bobbies on the beat – and wants a more efficient military that buys off-the-shelf Apache helicopters, not customised ones at five times the price.

A visceral scorn for the EU as the whipping boy for life's problems is what holds Ukip-ers together, but its agenda is widening.

Farage, 47, a former City broker turned MEP since 1999, and his executive chairman, Steve Crowther, a marketing man, know they must avoid the extremist and one-policy labels and reach out. There is little or no mention of China, India or even Germany, nor of larger economic or social forces at work. The tone is insular – and proud of it.

But Ukip is aware of one looming irony. For a party with its raison d'etre it knows that Alex Salmond's campaign to break up the UK must be a growing priority. On the conference fringe in Skeg the most heated debate was between those who advocate an England-only parliament to match the devolved assemblies, end the English backlash and save the union – and those who argued fiercely that such a strategy will "do Barroso's job for him" by breaking up Britain. Europe, it's everywhere.