I wonder if you could just add a link to a terms of service for your site that explicitly states the site was not for use by users in the UK, and that they should ensure they’re following all laws and using the site at their own risk.
- Show that you are aware of the regulation
- Implement some kind of thing to comply with the regulation. The degree of that is debatable and ultimately can only be decided by a court.
Just pointing to a ToS is not enough, because nobody reads them.
Implementing a geofence and denying service to UK ip addresses is probably a good start. If UK citizens want to access your service, they could still use a VPN, but then the "malice" is on them.
The bigger/widespread your service, the more effort you might have to put in to prevent malicious intent.
Think about this way: You are liable for the services you offer. You must comply with local laws. It's up to you how much liability you want to carry. If your compliance with laws is extremely weak, your liability is high.