We appreciate your first post here in the Roku Community, @Ten-a-c!
Thanks for reaching out. We'd be more than happy to help you access the Britbox channel on the other TVs in your house.
If you wish to access the Britbox channel on your additional Roku streaming devices or televisions, you should launch The Roku Channel application and locate the Britbox app.
You may check The Roku Channel application on your Home screen. Here's the photo for reference:
You may also visit this article to help you add this to your Home screen: How to add apps to your Roku streaming device
We hope this helps!
Warm regards,
Carly
Carly Y.
Roku Community Moderator