Whenever I try and search for some UK TV documentaries, the search comes back as negative. But when I manually search, for instance, the Pirate Bay, I can find literally hundreds of episodes. But on the Pirate Bay they are named ever so slightly differently.

For instance, I ask MCM to download new episodes for the program 'Horizon' and get no results. But a manual search finds hundreds listed as 'BBC Horizon'
The same for 'Panorama' there are hundreds never found because they are listed as 'BBC Panorama'
I would love it if the AI in Media Center Master could either allow me to set an alternative name under a TV program so whenever MCM searches for new episodes it would recognise 'BBC Horizon' as the same as 'Horizon'

Or am I a dimwit and this is possible already?

It would affect all future searches to whatever you set it to, but you can change the search term in on the metadata tab.

select the series then the metadata tab on right.