What channel are you watching the previous seasons on? If it's anything other than The Roku Channel, you would need to ask whomever provides that channel. If it is TRC, be aware that when Roku licenses content for streaming, they might be restricted by the content owner as to the seasons they can stream, and sometimes even individual episodes.
Since you mentioned it's a British series, perhaps it's available on BritBox. I know my sister-in-law loves watching content on that channel, and they do seem to offer most of the available British programming. They offer a free 7 day trial, although I don't know if the trial restricts access to any content.
Dan
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee, just another user.
