Shockwave This is outsourced and dealt with by Paddle - our third-party payment provider.
Actually, it looks like Paddle will send the billing reminder, depending on the location.
More details here: https://www.paddle.com/help/manage/your-customers/enhanced-billing-notifications-location-list
And specifically for the UK:
Regions in the United Kingdom
All regions within the UK require auto-renewal reminders for subscription periods of six months or longer.
*Please note that rules and regulations are constantly changing. We will be revising these notifications when needed, and will update this page accordingly.
So this means that users on the 3 month rolling plan have not received this, but users with an annual sub will, prior to their auto-renewal.