The Government said last night that it is committed to restricting children's access to pornography in video-on-demand services.

The Culture minister Ed Vaizey was responding to a report by the industry regulator Ofcom entitled Sexually Explicit Material and Video On Demand Services.

There are already strict controls on accessing porn on television and British-registered video-on-demand services that stream it online are protected by PIN to prevent children from viewing the content. But most online porn sites are not registered in the UK and have little or no restrictions on them.

Mr Vaizey said the continuing review of communications legislation would also focus on video-on-demand services. "Without a doubt we want to make sure that video-on-demand services carrying adult material cannot be seen by children and it's already a legal requirement that any such content has access controls," he said.

"The communications review gives us an opportunity to consider whether there's more we should do to ensure children remain protected and to limit access to potentially harmful material, such as introducing unclassified material into the statutory framework."

The internet is open by its nature, and ministers have struggled to find a way of restricting access for children.

Anti-pornography campaigners are demanding a new system where users would have to actively choose to receive adult content, rather than the current system where they can select filters. Internet service providers tend to prefer the idea that control of the internet should rest with parents.

New research published last month by the global entertainment consultancy Attentional found the appetite for video-on-demand services in the UK has stayed the same for 15 months with viewers preferring the reliability and better picture quality of television.

But of those who use video-on-demand services, a significant majority do so to watch porn. An estimated 57 per cent of internet video viewing is devoted to porn, while 37.8 per cent went to sites featuring videoclips and user-generated content like YouTube.

Just 4.2 per cent involved sites providing catch-up TV and other longform video-on-demand content; the remaining 1.1 per cent was taken up by music sites.