They are not UK based and won't consider themselves primarily a porn site so they may decide to risk it until they are warned. The law applies to any site where more than a third of "content" is porn, but it doesn't define how to calculate that. By one measure almost 100% of their pictorial content is porn so I am sure they should be covered by the checks. Expect them to offer their own fee-based checking service.
Looks like they will force verification for access
External Link/Members OnlyFrom their site
Anticipated March 2019 All UK Members Mandatory Age Verification
In April 2018 new regulation will come into force requiring that no adult content can be accessed by anyone who has not verified that they are an adult.
The latest information regarding the regulations and regulator can be found here:
External Link/Members OnlyAdultWork.com has been age-verifying members automatically since 2015. If you have purchased credits via SMS, credit card or PaySafeCard then you are already age verified and your browsing experience will remain unchanged. Similarly, if you are offering services and have achieved Verified Member status then you too will see no change.
If you have not age verified yet, we would invite you to do so without delay to ensure an uninterrupted browsing experience. You can age-verify quite simply via this page.