The move is intended to ensure that children are not exposed to sex as a routine by-product of the internet. It follows warnings about the hidden damage being done to children by sex sites.
The biggest broadband providers, including BT, Virgin Media and TalkTalk, are being called to a meeting next month by Ed Vaizey, the communications minister, and will be asked to change how pornography gets into homes.
Instead of using parental controls to stop access to pornography - so-called "opting out" - the tap will be turned off at source. Adults will then have to "opt in."
It follows the success of an operation by most British internet service providers (ISPs) to prevent people inadvertently viewing child porn websites. Ministers want companies to use similar technology to shut out adult pornography from children. Pornography sites will be blocked at source unless people specifically ask to view them.
TalkTalk, which includes Tiscali and the British version of Aol.com, is already introducing a new free service early next year called "bright feed," which allows people to control the internet so that all devices are automatically covered without the need to set up individual controls.
Homeowners can either specify which adult sites they want to receive or put a cinema-style classification on their feed to restrict what is received according to age ranges, such as U, 12 or 18. A survey by Psychologies magazine this summer found that one in three children aged 10 in Britain had viewed pornography on the net.
Mr Vaizey said: "This is a very serious matter. I think it is very important that it's the ISPs that come up with solutions to protect children.
"I'm hoping they will get their acts together so we don't have to legislate, but we are keeping an eye on the situation and we will have a new communications bill in the next couple of years."
Claire Perry, the Tory MP for Devizes and a keen lobbyist for more restrictions, said: "Unless we show leadership, the internet industry is not going to self-regulate. The minister has said he will get the ISPs together and say, 'Either you clean out your stables or we are going to do it for you'."
"There is this very uneasy sense for parents of children that we do not have to tolerate this Wild West approach. We are not coming at this from an anti-porn perspective. We just want to make sure our children aren't stumbling across things we don't want them to see."
Previously the Internet Services Providers' Association (ISPA) has told MPs that such a blanket ban would be expensive and technically difficult to operate.
But Miranda Suit, co-founder of the charity Safermedia, which held a conference on internet porn at the Commons last month, said: "Technically we know it can be done because the ISPs are already removing child porn after the government put pressure on them.
"In the past, internet porn was regarded as a moral issue or a matter of taste. Now it has become a mental health issue because we now know the damage it is causing. We are seeing perverse sexual behavior among children. Legislation is both justifiable and feasible."
She quoted the example of two underage brothers sentenced to at least five years' detention this year for a sadistic sex attack on two other boys in South Yorkshire. The brothers were said to have had a "toxic" home life where they were exposed to pornography.
This weekend some ISPs appeared ready to introduce an "opt in" clause voluntarily. Andrew Heaney, executive director of strategy and regulation for TalkTalk, said: "Our objective was not to do what the politicians want us to do but to do what was right by our customers.
"If other companies aren't going to do it of their own volition, then maybe they should be leant on. Legislation is a sledgehammer but it could work."
A spokeswoman for Virgin Media said: "We already have an opt-in approach on mobiles. We've taken this approach as mobiles are taken out of the home - and kept in a pocket - whereas parents can control what happens within the home and online "We're able to block sites, so it would be possible to do the same on the internet. It is just about finding the right approach."
A spokesman for BT, which has a "clean feed" system to block access to illegal sites, said: "We do what we can to protect children."
The ISPA did not return calls to London's Sunday Times.