In his keynote speech in Manchester, Ed Miliband taunted the prime minister for lying awake at night worrying not about the future of the United Kingdom but rather the United Kingdom Independence party. Badum-tish!

Like much of the speech the joke fell a bit flat because, as it happens, David Cameron isn’t the only one who has been losing sleep over Ukip. In previous years, the Labour conference treated the Faragist threat as private grief for Conservatives into which Miliband need not intrude. And it remains the case that Ukip takes more votes from the Tories. In a number of key marginal constituencies, Nigel Farage is making Labour’s work easier.

But that mechanical (and cynical) calculation is giving way to moral panic at the way Ukip campaigners are proselytising among traditional, white working-class communities.

Labour’s prospective parliamentary candidates (PPCs) at conference talk anxiously about a Faragist threat in their patch that has appeared suddenly and is growing rapidly. Fringe events on the Ukip menace were packed beyond standing room only. That used to happen at Tory conference. The fever is contagious.

There is some excitable talk about a serious threat to Labour in the Heywood and Middleton byelection on 9 October. The vote is on the same day as the Clacton contest where Douglas Carswell intends to ratify his defection to Ukip. Labour had hoped the higher-profile Essex race would allow them to fight a defensive battle on the outskirts of Manchester without attracting too much attention. But Clacton is in the bag for Ukip – Carswell’s triumph and Cameron’s humiliation are priced in already. So Farage can afford to throw a bit of campaigning muscle at Heywood. “We won’t lose the seat,” one well-connected local Labour campaigner tells me. “But we’re definitely in line to get a bloody nose.”

It is precisely with a view to capitalising on Labour discomfort that Farage has chosen Doncaster, Miliband’s own seat, as the venue for his party’s conference this week. Labour MPs and councillors who know the area a lot better than I do report alarming levels of voter flirtation with Ukip and ready contempt for Miliband – not sufficient to cost him his seat but perhaps enough to cause embarrassment and distraction in a general election.

Meanwhile, Labour campaign strategists are starting to lose hope of winning the Essex constituency of Thurrock, officially number two on the party’s list of target seats. The PPC there is Polly Billington, a former Miliband adviser. She is battling hard and has the support of an unofficial “save Polly” drive from friends on the frontbench. But Ukip is still winning on the ground.

The greater source of alarm in Labour circles is not so much the threat in individual seats, but what that threat reveals about the weakness of the Miliband message. Angry voters aren’t listening. Worse, they don’t want to listen because they judge instinctively that Labour’s high command is stuffed with people unlike them.

The party’s response is a campaign depicting Ukip as Thatcher on steroids, seeking to fleece and exploit hardworking people: “More Tory than the Tories”. My guess is that this line will have limited effect. Voters want to judge for themselves whether or not one party is like another – and many have already made up their minds that Ukip represents something new and different. Labour doesn’t have the authority to brand it as something else. And besides, telling people they are being duped is not an attractive message – it reinforces the suspicion that Labour is in the business of piously bossing people around, claiming to know what is good for them. It comes across as just another sneer from mainstream politics at the choices voters make.

Above all, Labour’s problem is a shortage of messengers who can deliver an anti-Farage line in tones and terms that resonate. There aren’t enough shadow cabinet ministers who look and sound as if their experiences equip them to understand the concerns of voters in Great Grimsby or Doncaster. There is plenty of youth and urbanity; not much grit and heft. That deficit explains why, whenever enough Labour people gather to lament their condition, the notion of bringing back Alan Johnson soon emerges.

Whether or not he would want a job, and what job that might be, are hardly relevant in the discussion. It isn’t clear who in the top tier of the shadow cabinet would move aside. That isn’t the point. The “bring back Alan brigade” don’t care what portfolio Johnson has. They want him installed as shadow secretary of state for working-class authenticity and having lived a bit. (There is a precedent for this kind of appointment. In 2009 Cameron brought in Ken Clarke as shadow minister for maturity and economic reassurance on the Today programme.)

In reality, the hankering for a change of personnel or a new attack line are proxies for a greater malaise. With seven months before a general election, Labour should be gearing up for battle. The annual conference is meant to inject vigour, infuse lifeblood. But the inescapable feeling in Manchester this year was that the energy in politics is flowing elsewhere and in another direction entirely.