Straight-to-download movies are to be given ratings by the British Board of Film Classification.
Until now there has been no obligation for such films to be given a certificate like cinema and DVD releases.
But now they are being given age ratings under a new Watch And Rate scheme to encompass the increasing number of films which do not have a physical release.
Online-only content is not covered by the Video Recordings Act but the BBFC has been working with video firms to develop a trustworthy labelling system.
It has already given 200,000 "back catalogue" titles a digital classification to provide information for video on demand and streaming services.
The new service will apply to digital-only content, as more companies turn to releases which bypass the costs of DVD or cinema.
The new scheme was welcomed by Creative Industries Minister Ed Vaizey, who said the internet had completely changed the way people accessed videos and music so it was “good to see the BBFC adapting to meet the demands of the online world”.
“Age ratings will help parents protect their children from inappropriate content and provide people with more confidence about the content they and their families are watching,” he said.
David Cooke, director of the BBFC said: "For parents it will offer labelling and content advice they know and trust in what is, for many, an unfamiliar landscape.
"We have an exciting part to play in the film and video industry's digital future. For almost 100 years we have supported innovation in the moving image industries, and our latest service is designed to support the ever-increasing technological development in our second century," he said.
Research has indicated that 91 per cent of parents want to see BBFC classifications on digital video content.