David Cameron has threatened to impose tough new laws on internet giants if they fail to blacklist key search terms for horrific images by October as part a new crackdown on online porn.

The Prime Minister set out a raft of reforms to protect children from "poisonous" websites that are "corroding childhood", including introducing family-friendly filters that automatically block pornography unless customers choose to opt-out.

Possessing violent pornography containing simulated rape scenes will be made a crime in England and Wales and videos streamed online in the UK will be subject to the same restrictions as those sold in shops. In a speech at the NSPCC headquarters in London, the Prime Minister acknowledged the issue of extreme and child pornography is "hard for our society to confront" and "difficult for politicians to talk about".

Family friendly filters will be the default setting for new broadband customers by the end of the year and only account holders will be able to change them. Existing customers will be presented with an "unavoidable decision" about installing the filters by the end of the 2014, Mr Cameron added. "We are not prescribing how the ISPs should contact their customers - it's up to them to find their own technological solutions. But however they do it, there will be no escaping this decision, no 'remind me later' and then it never gets done."

Experts from the Child Exploitation and Online Protection Centre (Ceop), which is set to become part of the National Crime Agency, will be given enhanced powers to examine secretive file-sharing networks, and a secure database of banned child porn images gathered by police across the country will be used to trace illegal content and the paedophiles viewing it.

But former Ceop chairman Jim Gamble, who resigned in protest over the merger with the National Crime Agency, warned the Government was not doing enough to deter paedophiles who shared abusive images of children online and claimed abusers would "laugh" at the porn filters.

The internet industry has agreed to use the database to proactively scan for, block and remove the images wherever they occur, Mr Cameron said. But he gave search engines including Google an October deadline to introduce further measures to block access to illegal content by blacklisting searches based on certain phrases, claiming they have a "moral duty" to act.

A Google spokesman said: "We have a zero tolerance attitude to child sexual abuse imagery. Whenever we discover it, we respond quickly to remove and report it. We recently donated five million dollars (£3.28 million) to help combat this problem and are committed to continuing the dialogue with the Government on these issues."

Mr Cameron's announcement was welcomed by women's groups and academics who had campaigned to close the "rape porn" loophole. Fiona Elvines, of Rape Crisis South London, said: "The Government today has made a significant step forward in preventing rapists using rape pornography to legitimise and strategise their crimes and, more broadly, in challenging the eroticisation of violence against women and girls."

Professor Clare McGlynn, of Durham University, said: "The extreme porn law can be swiftly amended to send a clear message that rape should not be a form of sexual entertainment. Reform of the extreme porn law represents an important shift in priorities away from consensual activity to challenging the sexualisation of violence against women."