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David Cameron's attempt to implement automatic porn filters could be scuppered by the European Union- and instead Internet companies may have to ask families if they want to be opted in or not.

A leaked document from Brussels, dated May 17, suggests 'managing web traffic' by default could be made illegal - including automatically applying parental controls.

The move has been met with outrage, with government internet safety advisor John Carr, describing the proposal from the EU as "sneaky" and "tacky".

(Image: PA)

Cameron wants a filter to be installed at server level, meaning it would be automatically activated unless the customer contacted the service provider and opted out.

He says the measure is intended for child protection, to prevent youngsters accidentally finding inappropriate content online.

But critics say it's the thin end of the censorship wedge, and will end up blocking far more than pornography.

Some believe web filtering will be included in Theresa May's 'anti-extremism' legislation, which is also said to give powers to allow Ofcom to censor television programmes before broadcast.

While the government say it's necessary to prevent the spread of extremist views, freedom of speech campaigners worry it'll be used to silence any opinion the government doesn't approve of.

Opt in filters have existed on mobile phones for nearly 10 years, with some internet providers also giving users the option of filtering adult content.

Currently, if you buy a new computer or update a broadband package, you generally get asked whether there are children in your household.

If you say yes, you are encouraged to set filters to restrict access to adult websites.