London ? The buttoned-up Brit may be a myth.

British people’s attitudes to sex and marriage have grown increasingly liberal over the last two decades, according to a study released Wednesday. But behavior has changed less than opinions.

The annual British Social Attitudes Survey said 70 percent of people think premarital sex is acceptable, while less than a third believe homosexuality is wrong.

In the 1980s, almost half of Britons surveyed disapproved of premarital sex and three-quarters thought homosexuality was always or mostly wrong.

“The heterosexual married couple is no longer central as a social norm,” said Simon Duncan, the report’s co-author.

Researchers said attitudes have been shifting gradually over the years.

Britain’s marriage rate is falling, with a corresponding rise in the number of unmarried people who live together. The 244,710 marriages in England and Wales in 2005 – the last year for which figures are available – was the lowest number since 1896.

Two-thirds of those surveyed felt there was little difference socially between being married and living together. Only 28 percent agreed with the statement “married couples make better parents than unmarried couples,” a figure largely unchanged since the question was first asked in 2000.

Duncan said views are more traditional when it comes to child-raising.

“When they are involved, alternative family arrangements are seen as less acceptable,” Duncan said.

Opinion on single parents was evenly split, with 42 percent of people saying one parent could raise a child as well as two, and 41 percent disagreeing.

Just under a third of respondents said two gay men in a couple can be good parents as well as a man and a woman; 42 percent disagreed.

Only 17 percent of men agreed with the statement “a man’s job is to earn money; a woman’s job is to look after the home and family” – down from 32 percent in 1989.

But behavior appears to have changed less than attitudes. More than three-quarters of respondents in heterosexual relationships said the woman does the laundry, a figure little changed since 1994.

“People are a lot more liberal in what they think, but it is still women doing the same things they did 20 years ago,” said another of the researchers, Elizabeth Clery.

Conducted by the National Center for Social Research, the survey interviewed 3,300 randomly selected adults across the country about topics as diverse as politics, the environment and racism.

Margins of error for sections of the report vary between two and three percentage points.

Thirty percent of respondents admitted to being biased against other races, saying they were “very” or “a little” prejudiced. That compared to 34 percent in 1985, but was up from 25 percent in 2000 – a fact researchers said likely reflected the impact of the Sept. 11 terror attacks.