Data shows that daily traffic to Pornhub, the UK's most used pornography site, has fallen from 3.6 million on July 24 - the day before the verification checks were introduced - to 1.9 million on August 8, a drop of 47 per cent.
Visits fell by 47 per cent and 39 per cent on XVideos and xHamster respectively over the same period - according to data from digital market intelligence company Similarweb.
The data shows the impact of the strict age verification rules from July 25 under the Online Safety Act.
However, social media platforms that have also introduced age checks for material restricted for under-18s, like X and Reddit, have not experienced dips in searches in the same timeframe.
A spokesperson for Pornhub said: "As we've seen in many jurisdictions around the world, there is often a drop in traffic for compliant sites and an increase in traffic for non-compliant sites."
The Online Safety Act contains rules on protecting children from harmful content that require sites and apps showing porn to prevent children from viewing it.
UK watchdog Ofcom has backed age assurance measures such as facial age estimation, which assesses a person's likely age through a live photo or video.
The act also orders online platforms to prevent children from seeing content including material that encourages self-harm and suppress the spread of dangerous online challenges.
This has led to issues such as age restrictions on an alcoholic recovery forum on Reddit, prompting warnings that the new law is over-regulating.
Ofcom insists that the act does not restrict freedom of expression and has highlighted provisions that are protective of free speech.
Violations of the Online Safety Act carry an array of punishments, ranging from formal warnings to a fine of up to £18 million or, in extreme cases, the site being blocked altogether in the UK.
The introduction of the age verification has sparked a surge in downloads of virtual private networks (VPNs) that enable people to circumvent restrictions on visiting certain websites.
