The adult content filters being rolled out by some internet providers under a scheme championed by David Cameron are blocking the websites of businesses and charities and are a “distraction” for parents seeking to protect children from online pornography, claim campaigners.

TalkTalk announced this weekend that it would follow Sky and become the second of the UK’s four major internet providers to roll out automatic filters for all its customers unless they specifically ask for them to be turned off. It plans to begin applying the blocks to all users’ accounts next month.

New customers will have the filter set on by default and will have to ask TalkTalk to allow pornographic and other adult content websites, including gambling, to be visited through their internet connection. Existing users can head to the company’s website to opt out.

TalkTalk’s HomeSafe, provided as a free option, can already stop internet connections from being used to access violent content and gambling websites, as well as pornography, if customers opt in for their household.

Sky said that its Broadband Shield software, which is provided to all of its customers, would be automatically switched on unless users had opted out.

Sky’s brand director, Lyssa McGowan, said the mandatory filters would be rolled out over the next 10 days. “Knowing our customers and the internet as we do, we believe this is the right and simplest solution to a problem we all know is out there,” she said.

The remaining two major providers, BT and Virgin Media, are coming under pressure to follow suit with content blocks. The prime minister has said that internet companies must do more to protect children.

BT said it is consulting its customers to ask them whether they want to have the tool introduced.

Virgin Media gives its users the opt-in option – to turn on the software if they want it.

The company has been sending its current customers on-screen messages about the filters which have been available since the summer, but voluntary take-up has remained less than 10%.

A Virgin Media spokesperson said the company was not reviewing its opt-in system: “We believe people should have the tools and advice to make the decisions that are right for them. This is why we invested in our Switched On Families guide and all our customers have been offered free parental controls, but it is their choice as to whether to use them.”

A report from Ofcom last July said that on average only 13% of new internet users opted to turn on filtering software that was offered to them.

But campaigners say that it is misleading to suggest these filters are just about blocking pornography, and that they block a range of content, such as drugs, sex, alcohol, tobacco and anorexia.

The Metropolitan police are currently producing a list of websites for the filtering services which they regard as terror-related.

A website discussing the legalisation of cannabis found itself blocked, as did several small wine dealers, said Pam Cowburn of the transparency campaign Open Rights Group. Last year research by the group found that 54 registered charities had their websites blocked by one or another of the filters.

Several were offering support and services to young people escaping abuse or alcohol dependency. One such charity, Alcohol Support, based in Aberdeen, called it a “big brother” approach.

“It’s still a problem; it isn’t being tackled in the rush to block what is deemed unsuitable.

“But it’s very simplistic: URLs with Sussex or Essex in them, for example, are blocked. It’s arbitrary and a blunt tool.

“There is no guarantee that all porn sites can be blocked, so parents can have a false sense of security that will actually stop them doing what they need to do, which is to talk to their children about the internet and about internet safety.”

Vicki Shotbolt, CEO and founder of social enterprise project the ParentZone, said: “Filters are at best a distraction from the most important way to look after your family online.” Open conversations and keeping informed were the way forward, she said.