Peers, MPs and church figures are among those who have signed the Safety-net petition demanding internet service providers (ISPs) be made to compulsorily block access to pornography on computers, mobile phones and tablets, organiser Premier Christian Media (PCM) said.

The petition, written as a letter to outgoing Culture, Media and Sport Secretary Jeremy Hunt, claims one in three 10-year-olds has "stumbled upon pornography online" and that youths aged 12 to 17 are the largest consumers of online porn.

It will be handed in to 10 Downing Street on Thursday by Safetynet representatives and a cross-party group of MPs, with a second copy sent to the Department for Education (DfE).

Peter Kerridge, the chief executive of PCM, said: "This simple measure would in no way restrict adults from accessing such websites by specific application but would help to protect generations of young people from online pornographers. We are now looking to this Government to take decisive action to halt this blatant and relentless assault on young and impressionable minds. We demand they lock this ever-open door to pornography and depravity."

In June, the Government launched a 10-week consultation asking parents and businesses for views on the best way to shield children from internet porn.

The study is also looking at measures to protect children from other sites such as those which promote suicide, anorexia, gambling, self-harm and violence.

Views on preventing online sexual grooming and cyber-bullying are also being sought, the DfE said.

Parents are being asked their views on three possible systems, including one where users have to opt in to see adult sites, and one in which customers are presented with an unavoidable choice about whether they want filters installed.

The third option would enable customers to block some content automatically but be given a choice to unblock them as they wish.