More than half of the UK’s top websites that were warned they faced enforcement action from the data protection watchdog over advertising cookies are now compliant with the law.

The Information Commissioner’s Office (ICO) said 38 of the 53 firms it issued a warning to in November have made changes to their advertising cookies to comply with data protection law, with four more committing to being compliant within the next month.

The regulator said several other organisation are working to develop alternative solutions, and it added it will provide further clarity on those cases in the next month.

Under UK data protection law, companies must give users fair choice to opt out of tracking using cookies, which are often then used to serve people personalised adverts online.

Companies are still able to show users adverts when someone has rejected all tracking, but the ads must not be tailored to the person browsing.

The ICO has previously issued guidance to help ensure firms make it as easy for users to reject advertising cookies as it is to accept all – often using consent banners which pop up when a user first lands on a website – but the watchdog said in November that some of the UK’s top 100 websites were not complying with data protection law on this issue.

The regulator wrote to these firms, giving them 30 days to comply or face potential enforcement action.

On the response to the regulator’s November warning, Stephen Almond, executive director for regulatory risk at the ICO, said: “We expect all websites using advertising cookies or similar technologies to give people a fair choice over whether they consent to the use of such technologies.

“Where organisations continue to ignore the law, they can expect to face the consequences.

“We will not stop with the top 100 websites. We are already preparing to write to the next 100 – and the 100 after that.”

Mr Almond added the ICO is “developing an AI solution” to help “accelerate” its efforts to spot websites using non-compliant cookie banners.

“Our advice to all organisations is to take action now to become compliant,” he said.

“We can already see the ripple effect of our intervention, with many organisations making changes to cookie banners without receiving a letter from us.

“As we’ll be steadily working our way through the list of websites offering services to UK users to give them all the same message, it makes sense to be compliant before the regulator comes knocking.”