Adults who want to watch online porn will be able to buy codes from newsagents proving they are over 18.

New age verification laws that are introduced this year will require viewers to prove they are not underage.

One option available to the estimated 25million Britons who regularly visit such websites will be a 16-digit code - or 'porn pass'.

The move is part of new legislation to prevent children accessing online porn.

While porn viewers will still be able to verify their age using methods such as registering credit card details, the 16-digit code option would be a fully anonymous option. Stock image

The new rules were due to roll out in April but the Government has delayed them to ensure any system introduced in workable.

Britain's film censor, the British Board of Film Classification (BBFC), has carried out a public consultation on how to go around enforcing the proof of age process.

While porn viewers will still be able to verify their age using methods such as registering credit card details, the 16-digit code option would be a fully anonymous option.

The cards will cost around £10 and could can also be used to purchase other age restricted products such as alcohol and knives.

However, shopkeepers could still ask to see documents, such as a passport or driving licence, before selling the 16-digit online access code.

It is hope he method will be popular among those wishing to access porn online without having to hand over personal details to X-rated sites.

It comes after a recent report showed how a total of 1.4million children clicked on pornographic websites in a single month - half aged six to 14.

While the new rules are designed to protect children, it will mean that an estimated 56 per cent of UK adults who in 2014 admitted to watching porn 'occasionally' will still have to prove their age.

Internet security expert and director of the Open Rights Group Alec Muffett, fears adults opting for more traditional methods to prove their ages could be leaving a digital trail.

He told the Telegraph: ' his legislation is a digital white elephant. The kids will beat the technology, and adults could have their details hacked.

'Nobody is lined up to guarantee the trustworthiness of the companies which provide age verification and confirm someone's age to a porn site.'

New age verification laws that are introduced this year will require viewers to prove they are not underage

David Austin, BBFC chief executive, said age verification was 'simpler than people think' and has been in use for other adult-only purchases.

He said viewers could expect to see a choice of age-verification options, typically from third party providers, meaning they will not have to share personal details with an X-rated site.

A spokesman for the Department of Culture, Media and Sport, the department which is introducing the legislation, said: 'We are in the process of implementing some of the strictest data protection laws in the world.

'A wide variety of online age verification solutions exist, or are in development, and they will have to abide by these high standards. We expect data security to be a high priority in the BBFC's guidance on age verification arrangements.'

The BBFC will not create the new age verification systems but will oversee their implementation.