Building and maintaining sexual relationships in the 21st century can be a minefield. It's common these days for people to expect partners to "perform" for them in front of webcams for "a bit of fun".Most of the time this is harmless and can help to "keep the passion alive" and strengthen relationships. But there's also a risk that the images could be used against them, if the relationship ends , for example.And if they're not sure exactly who they're performing for in the first place, there's an even greater risk of something going wrong.Worryingly, webcam blackmail, or "sextortion", is a growing phenomenon in the UK, according to figures released today by the National Crime Agency (NCA).Sextortion is when criminals use fake identities online to befriend victims and coax them into performing sexual acts via their webcam. The images are then used to blackmail them – pay up or see the intimate footage leaked to friends and family online.The crime is the stuff of modern day nightmares and many of us wouldn't wish it on our worst enemy.However, there's been a spike in the number of reported cases in the last year. The number of people who reported the crime more than doubled – from 385 in 2015 to 864 up to November 2016, the BBC reported The true figure is likely to be even higher because of the shame and embarrassment many victims feel about reporting the crime, the NCA said.