According to a new study, more people identify as bisexual than as gay or lesbian.
The poll says bisexuality is the next-most-common identity after being heterosexual.
Survey respondents from Generation Z, those aged 16 to 26, are the least likely to identify as straight.
Stonewall, the LGBT charity that commissioned the study, said the findings told a "positive story," but that more needed to be done to help bisexual people feel safe.
The study asked people aged 16 to 75 about their gender identity, sexual orientation, and attraction.
Three polls were conducted by market researcher Ipsos Mori in June, which is Pride Month, and August 2022, each with a representative sample of about 2,000 people from England, Wales, and Scotland.
When asked which label they identify with, 84% of all respondents said straight, 5% said bisexual, and 4% said gay or lesbian.
The responses varied according to age. 10% of Gen Z respondents identified as bisexual, compared to 2% of baby boomers (those aged 56 to 75).
According to Dr. Julia Shaw, a psychologist and author of the book Bi: The Hidden Culture, History, and Science of Bisexuality, it can be "frustrating" that many people do not understand what it means to be bisexual.
"It can cause you to experience biphobia and negative comments like, 'Oh, what does that mean? You're promiscuous? Or you can't be monogamous?" she says.
"Bisexuality is a genuine identity; it is not half gay, half straight."
She claims that trends over the last decade show that bisexual people are the largest "sexual minority," but that many people are unaware of how common bisexuality is.
Although the findings indicate that younger groups are more open to same-sex attraction, the apparent shift in attitudes may also give other generations more confidence.
John, 49, recently came out as bisexual.
The father-of-three admitted he'd known for a long time but dismissed it as "being straight with fuzzy edges" and "suppressing" his true feelings.
When asked which sex they are attracted to without labels like "straight," "gay," or "bi," only 66% of those polled said they were only attracted to people of the opposite sex.
Nancy Kelley, CEO of Stonewall, said the findings tell a "really positive story about the nation we are becoming."
"It tells us that lesbian, gay, bisexual, transgender, and queer people are more visible and connected than ever before," she added.
"When the label is removed entirely, you get an even larger community of people saying, 'you know what, I can be attracted to different kinds of people.'"
She said it was "really welcome" that bi people were becoming "much more visible," but she added that biphobia remained "really prevalent."
"We've got a lot of work to do to make sure that bi people feel safe, sharing who they are with us and being out in their day-to-day lives."
The findings, released by Stonewall on Thursday, show a similar trend to UK official statistics, with a slow decline in heterosexual people. Because the questions are worded differently, the official statistics on bisexuality could not be directly compared.
Another study finding was that 2% of respondents said they are asexual, which means they have little or no sexual attraction to anyone.
Yasmin Benoit has been an asexual since she was 15 years old.
One of the "most common misconceptions" she's encountered is that asexual people must have "something physically or mentally wrong, such as a personality flaw, a hormone deficiency, or a mental disorder."
But she says being asexual means she can "just focus on all the other joys of life" instead of worrying about "navigating sexual situations".
"It definitely doesn't limit me in any way."
Yasmin Benoit says there are misconceptions about asexuality
In terms of gender identity, less than 3% of those who participated identified as transgender or non-binary.
According to the most recent government statistics, there are between 200,000 and 500,000 transgender people in the United Kingdom.
When the results of the 2021 Census for England and Wales are released later this year, they are expected to provide a more detailed picture of the population's make-up.