Social media firms could be banned if they fail to protect children from suicide and self-harm material, the Health Secretary has warned.

Matt Hancock said Parliament had the power to block access to the social networks and that the Government "must act" if tech companies failed to purge their sites of such images and videos.

His comments come as a Daily Telegraph investigation has found Google promoting graphic suicide manuals high up in its search results and YouTube has allowed advertising on videos showing suicide methods.

Both companies feature the Samaritans' telephone number, and YouTube has since pulled advertising from the clips.

Speaking on The Andrew Marr Show on Sunday, Mr Hancock said: "If we think they [social media companies] need to do things that they are refusing to do, then we can and we must legislate.