Automatically blocking access to hardcore pornography online will not stop the images falling into the hands of children, a police chief has said.
Children who want to look at pornography online will always be able to find a way to do so, just as they did before the internet, Peter Davies, the lead on child protection for the Association of Chief Police Officers (Acpo), said.
Bringing in automatic filters would be no substitute for "sitting down and having proper conversations with our kids", he warned.
"The issue for me is that I don't think it will stop children having access to pornography, which I think is what people would like it to do," he said.
"Children will find a way on the internet - just as, frankly, those that wanted to generally found a way before the internet existed.
"As a risk mitigation tool I have no problem with it and I think it will help some children in denying them access to material they shouldn't see.
"I don't think it will stop children accessing pornography online."
Parents and others would still need to educate children "who may well be exposed to material whether we like it or not", he added.
"We're dealing with human behaviour. I don't see any problem with what's being proposed in terms of denying some children access to pornography, but it won't be the whole answer.
"We've still got to end up sitting down having proper conversations with our kids about how to deal with that material responsibly because it's still a risk that they might access it."
Mr Davies, who is also chief executive of the Child Exploitation and Online Protection centre (Ceop), went on: "I don't think we should underestimate the ability of people who are able and adept at operating the internet to get to what they want to get to regardless of what filters are put in place.
"So I see it as a useful risk-mitigation measure, if it proves to be acceptable.
"I don't think it will stop pornography falling into the hands of children, for example. Nor will it, of itself, stop the circulation or availability of child abuse images."
Giving evidence to the Commons Home Affairs Select Committee, he agreed with Deputy Children's Commissioner Sue Berelowitz that access to online pornography was "normalising" some abuse.
But he added: "I don't see it as the overriding issue, the overriding driver behind child sexual exploitation.
"It's a risk, it's a concern, but there are other bigger factors at play."
Mr Davies went on: "The level of exposure to pornography that's available on the internet can be harmful for children who access it, and actually can be harmful for anybody who is vulnerable to that kind of thing.
"Clearly it has a role to play in normalising or making people think that some types of behaviour are appropriate when sometimes they're not.
"I do see it as an issue."