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.
Re: Bought the ROKU premiere to replace our NOW TV white box but can't add it?
I'm not in the UK and I know little to nothing about NOW TV, but for regional channels like that everything has to check out to be able to add and use them. Your account must be created in the UK and you must be located in the UK and sometimes I think even the device itself matters (I've seen CA and EU after device model numbers, but I don't know what if anything they mean as far as adding channels). If all that's already true, the only thing I can suggest is to start over. Factory reset your Roku from Settings->System->Advanced system settings and relink it. Make sure you use https://roku.com/link - I imagine that will redirect to the en-gb version of the activate page.
If it still doesn't work, consider creating a new Roku account. Make sure you're not using anything that would hide your true location (like a VPN or proxy).