But Sarah Hunter, the website’s head of UK public policy says the proposal would “overblock or underblock”, while also “deskilling” parents, the Daily Telegraph reports. “Legislation would be a mistake,” she said.

Having parents to talk to young people while they were using the web would be a better way to protect children from seeing inappropriate material online, Ms Hunter claimed.

“The best thing we can do is make sure parents sit with their children on the internet when they’re very young and have conversations with older children about sex in general,” she said. And she pointed out that earlier Government campaigns such as Get Safe Online have previously advocated that approach.

David Cameron, the Prime Minister, is said to prefer a system which would encourage parents to make “an active choice” about what their children can see online when they sign up for a broadband package.

Currently only one UK internet service provider, TalkTalk provides a filter at a "network level", but Andrew Heaney, the firm’s head of strategy and regulation, admitted that it could be bypassed by “any intelligent teenager”. He said TalkTalk was not presenting the technology as a “silver bullet”.

“They do stop some forms of content but there’s lots more beyond filters that needs to be done,” said Heaney. “The Government should be encouraging ISPs to offer filters, in the same way they should be encouraging device manufacturers to offer ways to protect children; but they shouldn’t be forcing it on people, because that would be crossing the Rubicon into censorship.”

Ms Hunter said: “We at Google also believe that children shouldn’t be seeing pornography online. None of us don’t want children to be safe online. What we disagree with is the mechanisms by which we protect our children. It’s not that easy and the solutions that are being discussed are not perfect.”

Reg Bailey, the head of the Mothers’ Union, was commissioned by Downing Street last year to hold a review of the sexualisation and commercialisation of children.

Mr Bailey recommended the “active choice” compromise for web services. A group of MPs, led by the Conservative Claire Perry, has called on ministers to go further. Mrs Perry said: “If British Internet Service Providers introduced 'opt-in’, we would be the first country in the world to have such a system. The time for common sense solutions is here. We have got to act.”

Meanwhile, a UK police child protection expert has warned that children as young as five need to be educated about the risks of ‘sexting’ their friends.

Peter Davies, Chief Executive of the Child Exploitation and Online Protection Centre, told MPs that young children were sending sexually explicit images of themselves to each other, in a practice known as ‘sexting’, and children under eight need to be warned about the growing trend.

Mr Davies believes it is too easy for youngsters to stumble across indecent images on the web which they could copy themselves through means of sexting, according to the Daily Mail.

His organisation is now sending films to schools aimed at children between five and eight, to train them how to avoid the online dangers.

Giving evidence to the House of Commons Education Select Committee Mr Davies said there was a lack of urgency on the part of police to improve things.

He added: “But the police service doesn’t act on its own, and I think the best leadership for tackling this on the ground is local leadership.”

He told MPs ‘sexting’ was a growing problem, but only a fraction of incidents where it had “gone wrong” were reported to police.

An NSPCC study of sexting found that teenage girls are coming under increasing pressure to text and email explicit photos of themselves.

The charity said that more than a third of under-18s are believed to be affected by it.

According to research presented at the Westminster Education Forum last year four in ten children between the ages of 11 and 16 are aware of sexting taking place at their school.