Pornography websites will be forced to prove that users are aged at least 18 under tough new powers to be announced by the Government tomorrow.

The websites will have to install age-verification software or risk being banned in the UK. Sites could also face £250,000 fines if they fail to comply.

It is estimated one million children access pornography websites each month. An NSPCC study found half of secondary school pupils had watched online pornography, which experts warn gives them a warped view of sexual relationships.

Damage: Experts say online pornography warps children's views of relationships (stock image)

The Government will also announce to Parliament that it plans to appoint a regulator to police the sex websites. It is believed this could be the British Board of Film Classification – which sets age limits on films, DVDs and video games.

It is understood porn site users will have to provide details from their credit card, which cannot be legally issued to anyone under 18. Gambling websites use the same system of verification.

Digital Minister Matt Hancock said: ‘We are taking the next step to put in place the legal requirement for websites with adult content to ensure it is safely behind an age-verification control.

‘All this means that while we can enjoy the freedom of the web, the UK will have the most robust internet child protection measures of any country in the world.’

The NSPCC’s study found that 48 per cent of 11- to 16-year-olds had viewed online pornography, which experts say is highly damaging to children’s development and can cause lasting harm.

The NSPCC’s study found that 48 per cent of 11- to 16-year-olds had viewed online pornography (stock image)

The new Government powers will apply to both free and paid-for websites set up by commercial porn companies, as well as sites hosted abroad. Ministers hope the changes will be in place by April next year.

Will Gardner, chief executive of internet safety charity Childnet International, said: ‘Protecting children from exposure, including accidental exposure, to adult content is incredibly important, given the effect it can have on young people.

‘Steps like this to help restrict access, alongside the provision of free parental controls and education, are key.

‘It is essential to help parents and carers, as well as young people, be more aware of this risk and what they can do to prevent exposure and also to make sense of exposure if it happens.’