T HE 22 OFFICIAL surveys that estimate the number of lesbian, gay and bisexual Britons would disgrace the back of an envelope. According to one, 0.9% of Britons are not heterosexual. Another puts that figure at 5.5%. Guesstimates for the transgender population are fuzzy, too. The government “tentatively” reckons there are 200,000-500,000. So Lisa Power, who co-founded Stonewall, an LGBT charity, says she is delighted that statisticians plan to ask for the first time about sexual orientation and gender identity in the next census, in 2021. “If you don’t count, you don’t count.”

Policymakers will find the figures helpful. LGBT folk have more mental-health troubles than straight people, says Paul Twocock of Stonewall. Wonks armed with data ought to be able to meet this demand more accurately. The government struggles to budget for policies to promote minority rights, like those that allow gay marriage or ban employment discrimination. Census data would let councils see the extent to which such minorities were represented in their areas. Doctors’ surveys suggest an uneven spread among London boroughs, for example. One in ten residents in Lambeth—which includes Vauxhall, a gay hotspot—say they are not straight, compared with one in 70 in Havering.

LGBT- rights campaigners are chuffed. Some suspect the census may reveal there to be more transgender folk than widely thought. “There might be a huge, submerged section of the population,” says Matthew Parris, another co-founder of Stonewall. Exposing it could normalise transgenderism, he says.

Yet there could just as easily be an undercount. The census is filled in by the head of household, who might wrongly assume other members are straight. (To avoid awkward conversations at home, the authorities will let people answer sex and gender questions themselves if they prefer.) And unlike most census questions, the new ones will be voluntary. “It might not catch quite a lot of people who feel prickly or private,” says Mr Parris.

Other respondents may misunderstand what they are being asked. In one survey, some older gay men said they had changed gender identity when they simply meant they had come out. The government may find that if it asks queer questions it gets some queer answers.