Virtual private network (VPN) apps have become the most downloaded on Apple's App Store in the UK after sites such as PornHub, Reddit and X began requiring age verification of users on Friday.

VPNs can disguise your location online - allowing you to use the internet as though you are in another country.

It means that people are likely using them to bypass requirements of the Online Safety Act, which mandated platforms with certain adult content to start checking the age of users.

As of Monday morning, half of the top ten free apps in Apple's app download charts in the UK appeared to be for VPN services.

And one app maker told the BBC it had seen an 1,800% spike in downloads.

Virtual private networks connect users to websites using a remote server and conceal their actual IP address and location, meaning they can circumvent blocks on particular sites or content.

Platforms allowing porn and other forms of content deemed harmful to children are required to use "robust" methods of checking whether users are over or under 18.

These include requiring someone to take a selfie or video of their face to facilitate facial age estimation, or upload a form of ID - leaving some people concerned their data could be retained, used or linked to other web activity.

But experts say free versions of VPN apps or services may carry security and privacy risks.

"Many of these free VPNs are riddled with issues," said Daniel Card, a cyber-security expert with the Chartered Institute for IT (BCS).

"Some act as traffic brokers for data harvesting firms, others are so poorly built they expose users to attacks."

He told the BBC despite posing a range of potential privacy risks, such apps "end up in the hands of kids trying to watch age-restricted content", or adults "trying to get round blocks".

"That's the uncomfortable truth: people will take risks to get what they want online," he said.

The UK's new online safety rules, explained:

Katie Freeman-Tayler, of children's safety group Internet Matters, said on Thursday that availability of free and low cost VPN services to children, and their potential use of them, was "concerning".

"This makes it easy for them to circumvent important protections introduced under the Online Safety Act, such as age checks designed to shield them from adult content," she told the BBC.

But Ofcom says platforms required to introduce "highly effective" methods to check user age must not host, share or permit content that encourages use of VPNs to get around age checks.

The government has also told the BBC it would be illegal for platforms to do so.

Proton VPN, an app offered by Swiss privacy tech firm Proton, told the BBC it had seen a 1800% spike in UK daily sign-ups over the weekend after age check rules took effect on Friday.

A Proton spokesperson said the UK was now among countries generating the highest usage of its VPN.

"This clearly shows that adults are concerned about the impact universal age verification laws will have on their privacy," they added.

Rajat Vaghani, vice president of engineering at Free VPN - the sixth top free app on the App Store as of Monday - said it had also seen "a significant surge" in new UK-based users and downloads over the weekend.

It and other free VPN apps appearing in the App Store's top charts on Monday say they display adverts in order to finance and operate their services for free.

Some say they do not share information with third-parties, and state they are not intended for use by children. All state their VPN connections are private, secure and encrypted.

"While more privacy-conscious users might stick to reputable services... the average person won't," said Mr Card.

"They'll download the first free app with decent reviews, often without realising they're handing over access to their data."

Additional reporting by Chris Vallance.