The UK's porn filters could be made illegal under a proposed EU law heading for a vote in the European Parliament this autumn.

The law takes aim at roaming charges but it will have far-reaching implications for net neutrality and the UK's adult content filters introduced in July 2013, say legal experts.

It boils down to the fact that "if you're a German customer who wants specific content, you should be able to access it in the UK as well", said Denis Keseris, a patent attorney who specialises in information and communications technology as a partner at the firm Withers & Rogers.

Approved on 30 June, the Single Telecoms Market law marks the end of mobile phone providers' roaming charges throughout the EU from June 2017 onward. The new laws will also "enshrine the principle of net neutrality into EU law". That means "no blocking or throttling of online content, applications and services".

The European Parliament, Council and Commission agree that "until now, there have been no clear rules on net neutrality at EU level" and that "we cannot afford that 28 Member States adopt 28 different approaches on that issue".

What they aim to do is "introduce for the first time rules safeguarding the open Internet in the EU", according to a EU statement on the law. The regulations oblige each EU member state to "set rules on the penalties applicable to infringements of the net neutrality provisions". Failure to do so could expose them to a lawsuit.

It means that by law, "service providers in Germany are forced to provide the same level of service to British travellers" and vice versa, said Keseris.

Opt-in basis for adult content

For the past two years, the UK's internet service providers have been operating on an opt-in basis when it comes to certain adult content. Prime Minister David Cameron announced in July 2013 that pornography and gratuitous violence must be automatically blocked by ISPs whose customers then choose to opt-in to view it.

The new law would put an end to the UK "porn filter" as internet service providers would be barred from filtering such traffic from the start. Mobile phone operators in the UK have been using opt-in pornography filters for the past 10 years.

A draft of the new law leaked on 17 May drew condemnation from John Carr, the government adviser on internet safety.

"The risk is that a major plank of the UK's approach to online child protection will be destroyed at a stroke," he told the Sunday Times. "It all seems a bit sneaky or tacky for this to have come about as the result of a measure which, ostensibly, has nothing whatsoever to do with online child safety."

He argued that "parents should not have to jump through hoops to make the internet safer."

It all seems a bit sneaky or tacky for this to have come about as the result of a measure which, ostensibly, has nothing whatsoever to do with online child safety - John Carr

Yet the law may not be as wide ranging or clear cut as it seems, said Cris Chesha leader of the UK's Pirate Party. In the language of the law, "there are clear exceptions for court ordered IP blocks, and 'measures implementing this legislation such as a decision by public authorities', so there is no effect on either IP blocks or the government's objectionable content filters".

He called the new rules just "a small step in the right direction for consumers in that ISPs can no longer throttle connections" to allow preferred content to be delivered faster.

Chesha argued against the law's use of the phrase "net neutrality," stating the EU "should have no right to use the term". While these rules "claim to 'enshrine the principles of net neutrality into EU law'", he said: "That couldn't be further from the truth."

He picked out the law's tiered network for specialised services and "zero rated" content that is not marked against a customer's bandwidth limit as aspects that fly in the face of "the very definition of non-neutral networks".

A spokesperson for UK's communications regulator Ofcom said that so far, the organisation has no evidence "of consumer harm arising from current practices". What providers need to do, they said, is "be transparent about their policies".

They added: "Internet providers need some flexibility in running their networks for the benefit of consumers – for example, to block illegal content or to manage user traffic efficiently."