More than half of Britons say you can't deny sex once undressed

More than half of Britons do not think it is acceptable for a person to refuse to have sex once they are naked with a potential partner, a survey by a sexual health charity found.

More than half of Britons do not think it is acceptable for a person to refuse to have sex once they are naked with a potential partner, a survey by a sexual health charity found.

The Family Planning Association (FPA) said its survey had revealed "deeply concerning attitudes", with many people also saying it was not fair for someone to turn down sex if they had been bought drinks, or had already kissed the other person.

"It's really worrying that people of all ages think that it's not OK to withdraw consent in a range of situations," Natika Halil, chief executive of the FPA, said in a statement.

"It's always OK to say no to sexual activity that you're not comfortable with, whatever the situation."

The research comes amid widespread public debate around the issues of consent and sexual violence faced by women, triggered by the #MeToo campaign which has seen a slew of high-profile figures accused of sexual misconduct over the last year.

The survey of 2,000 people - published to mark Sexual Health Week in Britain - found young people were most likely to think it was unfair to withdraw sexual consent in some circumstances.

About 60 percent of teenagers aged 14-17 and nearly three-quarters of people aged 25-34 said it was too late to say no once undressed, compared with 30 percent of adults aged 45-54.

The "deeply troubling" findings show how much work is needed to educate people about consent, Katie Russell of charity Rape Crisis England and Wales told the Thomson Reuters Foundation.

"It's crucial we start educating children from the earliest possible age about consent and bodily autonomy if we're to stand a chance of reducing and eventually ending the chronically high levels of sexual violence in this country," Russell added.

One in five women in England and Wales have experienced sexual assault since the age of 16, government data show.

Sweden outlawed sex without mutual consent in May and Spain has pledged to pass similar legislation, joining a small number of nations, such as Britain and Canada, where lack of consent is considered a crime without the need to show threats or violence.

A Dutch startup launched an app this year which uses blockchain to record sexual contracts between partners via their mobiles, confirming they both consent and outlining conditions.