So it was only matter of time before a mobile phone app was launched that lets people say yes to sex.

The app is designed to make sure there's no trouble between partners the morning after the night before, as they film themselves giving consent. But while some health workers have backed so-called 'sex contracts', rape victims and student union leaders have condemned them as 'evil' and 'dangerous'.

The WeConsent app is available for £3.20 and is the creation of former Wall Street banker turned philosophy professor Michael Lissick. It uses an Apple iPhone's video camera to make a 20-second recording of both partners agreeing to sex.

A breathy female British voice asks participants to state their name and to agree to sex. Once the video has been completed the voice says: 'Consent confirmed. Have fun.' The video is then saved in a 'cloud' or server.

Mr Lissick, 57, said: 'The videos are twice encrypted and can only be accessed by law enforcement, by a written judge's order or as part on an ongoing sexual investigation by a college.'