ASKED to describe Boris Johnson, the eight Remain voters gathered around a table in a conference room in a shabby hotel in Sutton Coldfield do not hold back. “Troublemaker.” “Egotistical.” “Idiot.” “Laughing stock.” “Malicious.” Nor do the group of Leave voters who enter afterwards have a particularly high opinion of the former foreign secretary. “Goof.” “Joke.” “Buffoon.” “Selfish.”

Focus groups provide a bracing introduction to the great British public. In an era when voters are monitored, tracked and polled more than ever, they may seem anachronistic. Yet they thrive. Demand for focus groups has held up for a simple reason, according to industry executives. Wide-ranging surveys explain what the British public think, says Michelle Harrison, chief executive of Kantar Public, a pollster. Focus groups explain why they think that way.

On the face of it, focus groups have as much credibility as water dowsing. It is an unscientific exercise. A local recruiter rounds up between six and a dozen people, whose main qualification is a willingness to sacrifice an evening to discuss politics in exchange for about £40 ($50) in cash or gift tokens. The politico or pollster leading the discussion will break the ice and then take them on a tour of British politics, gauging their reactions to slogans or politicians. “It’s about feel,” says one pollster. “Seeing the whites of their eyes.”

It is the mixture of large-scale surveys and smaller in-depth chats with voters that provides insight. Relying on only one leads to trouble. “If you do either on its own, you’re stuffed,” says one former member of the Vote Leave campaign. Attention has focused on Vote Leave’s online activities, which broke spending limits before the referendum, according to the Electoral Commission. But the campaign’s organisers hail more bog-standard techniques, including the relentless use of focus groups, in which their (and their opponents’) slogans and adverts were tested repeatedly.

Focus groups are far from perfect. Rory Sutherland, an advertising executive at Ogilvy, quotes his firm’s founder: “People don’t think what they feel, don’t say what they think and don’t do what they say.” The success or failure of a group is determined by the stewardship of its leader, says Sophia Gaston, a visiting research fellow at the London School of Economics. But focus groups’ strength is in teasing out answers to subtle questions of culture and identity, she adds.

Under Tony Blair, Labour was criticised for over-relying on focus groups, with political principles thrown out of the window at the behest of a small number of voters in Middle England swing seats. “They’re a relic,” says one organiser of Momentum, a left-wing Labour activists’ group. “A dialogue is what you want, not policy written for a small bunch of people in Hastings.” Yet even under the party’s new management, focus groups survive. For all Jeremy Corbyn’s insistence on a new politics, his team still uses focus groups to test slogans and certain phrases.

Rather than wither away, de facto focus groups may find themselves embedded into Britain’s constitution. In a bid to jazz up local democracy, the government is toying with the idea of “citizen juries”, small panels of voters who would have a say on policy. After all, a dozen punters pulled off the street determine whether to send someone to jail. By comparison, asking their opinion on a political slogan or a new housing development is small fry. In an age of big data, small data still has a place. Mr Johnson can expect similar pastings in such groups for a long time yet.