PM says there is a distinction between images online, which he is trying to tackle with filters, and those in a newspaper

David Cameron has insisted he is right to oppose a ban on Page 3 pin-ups despite his efforts to tackle online pornography. The prime minister said there was a difference between newspapers, which parents could keep away from children, and the internet, where youngsters could "stumble across" legal but hardcore pornography.

Under plans set out by Cameron, the largest internet service providers in Britain will force customers to choose whether to turn off filters that will prevent customers viewing porn.

In an interview with BBC Radio 4's Woman's Hour he insisted there was a distinction between images online and in the pages of a newspaper.

He said: "I've said what I've said about Page 3 and the Sun and I haven't changed my views. But should we do more to try and help parents to protect their children from legal pornography on the internet? Yes I think we should, and again last week we made some big progress on that."

Cameron added: "You can control your children's access to newspapers and books and magazines. The problem with the internet is that our children are all online and they're using YouTube and they're searching for videos and the rest of it and there's a danger that they can stumble across really quite, sometimes hardcore legal pornography."

The plan set out with BT, Virgin, Sky and TalkTalk was about "making sure every household is offered a default-on filter to stop those images coming through, and that's what we've enabled".

He added: "I think there's a difference between a physical product as I said and the internet and that's why I think this specific action is needed on the internet and that's why I'm driving that.

"I've answered the question about Page 3 before and I don't believe in intervening in that but the internet is different because our children are on it. They're in it. They're searching for things and there is a danger and I've seen this happen of children finding things on the internet quite opposite to what they're looking for but often very shocking."

Cameron said he had talked to parents who had experience of their children performing legitimate searches but finding "some pretty horrible things in front of them".

Explaining the move to a default filter setting, he said: "I think it's better to say, look, when you switch on your computer, when you've got a new broadband connection, the filters are on. They're ticked on. Do you want to tick them off?

"I think that's the right way to do it and we're going to do that of course not only with existing customers but also new customers too. So that will as I say get through to something like 80%-90% just with those four companies alone."

The interview can be heard on Woman's Hour on BBC Radio 4 on Saturday at 4pm.