Britons are becoming more sexually adventurous, with fewer defining themselves as "straight" and an increasing number answering "don't know" when asked to define their leanings.
The annual Integrated Household Survey (IHS) published by the Office for National Statistics (ONS), found a record number of people answering: "I'm sorry I haven't a clue," when asked about their sexual identity.
The survey found that 94 per cent of adults defined themselves as straight, a 0.2 per cent fall.
The figure for heterosexual men dropped by 0.4 per cent to 93.6 per cent. Women identifying themselves as straight fell by 0.2 per cent to 94.3 per cent of the population.
The IHS, the largest social survey published by the ONS with 420,000 respondents, identified 1.3 per cent of men as gay with 0.6 per cent of women claiming to be lesbian. The combined gay and lesbian population is 1.5 per cent of the total. Those answering bisexual accounted for 0.5 per cent.
But the largest rise, by 0.4 per cent to 3.6 per cent among men and women combined, was for those who, given a choice of sexual identities, answered: "Don't know". A total of 4.3 per cent said they would not or could not answer the question.
Matthew Todd, editor of gay lifestyle magazine Attitude, claimed sexual identities are becoming more fluid.
"There is a trend for people refusing to be put in a box," he said. "I met someone recently who said they were 'polysexual'. They had an ongoing relationship with a man and a woman. There are so many lifestyle choices it's understandable if people are confused."
Mr Todd added that the 1 per cent figure "seriously underestimated" the total gay population in Britain.
He said: "It still isn't entirely socially acceptable to be gay, so there will be young people who have yet to reach that conclusion themselves, or don't feel comfortable identifying themselves as gay."
The south west has the UK's largest bisexual population, with 0.9 per cent placing themselves in that category, compared to 0.2 per cent in Northern Ireland. London has the most gays and lesbians, while the "straightest" region is the north east with 95.9 per cent resolutely heterosexual.
Younger people are more likely to describe themselves as gay or lesbian, with 1.4 per cent of the 25-34 age group doing so, compared to just 0.3 per cent of people aged 65 and over.