The company confirmed the change and also explained it will go further by emailing all existing customers, asking them if they would like the filter to be switched on.
Lyssa McGowan, Sky’s brand director for communications products, said: “We believe that this ‘default on’ approach will mean much greater use of home filters and ensure a safer Internet experience for millions of homes.
“It came about as we looked for the best way to meet the Prime Minister’s objective of providing more protection for children when they use the Internet.”
The ISPs landmark decision comes after David Cameron called on the Internet service providers to take action.
Responding to the announcement, Child’s Eye Line UK’s founder Kathy McGuinness, said: “We are delighted that Sky has taken this important voluntary step to protect children in the UK. We have campaigned hard on this issue for three years and believe it reflects the depth of the public’s concern about children’s easy access to harmful content online.
“As the major ISPs own figures show, the voluntary system of self-regulation is not effective in providing adequate protection for children.
“Sky has acted responsibly in recognising the urgent need to provide proper protection for children online to prevent needless exposure to harmful adult content.
“Unfortunately, however, there is still more work to be done as the default-on filters for all new customers still falls short of what is needed to protect children.
“Child’s Eye Line UK is campaigning for a statutory requirement for all Internet service providers to ensure default on filters with robust age-verification are in place to make sure only adults who can prove they are over 18 can turn the filters off.
“The government has made a manifesto commitment to improve the protection of children online and it is essential in the New Year they keep their promise and take urgent action.”
Ofcom figures obtained earlier this year showed Sky customers were the most active when it came to using content filters, with more than 30% leaving content filters switched on, while none of its rivals – BT, Virgin Media and TalkTalk – had reached 15%.
Sky added that 62% of the customers it had sent the “unavoidable decision” email to had kept some form of parental control turned on.