Prime Minister David Cameron has welcomed moves by Microsoft and Google to help block child porn, as he hosts a Downing Street summit today to discuss web child protection.
Cameron said internet search engines in particular have made "significant progress" since July to prevent child abuse content from being available, but he said legislation would be brought forward if the ISPs and other main players "fail to deliver".
He said Google and Microsoft have introduced a number of changes to their search function, not only in the UK, but across the world. UK National Crime Agency testing of the new measures shows that child abuse images, videos or pathways are no longer being returned against a blacklist of search terms, at present.
New algorithms have been introduced by Google that block child abuse images, videos and pathways that lead to illegal content, covering 100,000 unique searches.
Auto-complete features offering people child abuse search terms have also been blocked.
Google and Microsoft will now work with the National Crime Agency and the Internet Watch Foundation to bring forward a plan to tackle peer to peer networks featuring child abuse images
Google will also introduce new technology that will put a unique identification mark on illegal child abuse videos, which will mean all copies are removed from the web once a single copy is identified.
Cameron said: "Back in July, I said I wanted to do much more to protect our children from the risks posed by the internet and those who seek to use the web to look at and share illegal and vile content.
"Since then we've strengthened Britain's ability to combat child abuse online with the new National Crime Agency, with over 4,000 specially trained officers."
He threatened legislation, however, if more wasn't done. Cameron said: "With the progress that has been made in four months, I believe we are heading in the right direction.
"But no-one should be in doubt that there is a red line: if more isn't done to stop illegal content or pathways being found when someone uses a child abuse search term, we will do what is necessary to protect our children."
Downing Street said the main ISPs will confirm to the prime minister that 20 million homes - 95 percent of all homes in Britain with an existing internet connection - will be required to choose whether to switch on a whole home family friendly internet filter by the end of next year.
The six largest public WiFi providers across Britain have also switched on family friendly filters in all areas where children might access the internet.
Britain and the US have teamed up to target child abuse online with a new UK-US taskforce, set up between the US assistant attorney general and the UK government.
And ex-Google and Facebook chief Joanna Shield will lead an industry group of technical experts to explore what more can be done.