Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
I'm not 100% certain about Britbox, but very few providers allow access to their content in any way other than authorized apps. Most providers use DRM (Digital Rights Management) that restricts the media from playing on anything other than an authorized app or computer browser that is logged into a user account.
If there's any way to do it, it's most likely breaking copyright laws, which makes it illegal.
Dan Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.