M.I. High was a British children's television series that aired initially on the BBC's children's network CBBC from January 8, 2007 to March 21, 2011, spanning five seasons. It was subsequently revived for two more seasons in 2013-2014, but was cancelled suddenly in 2015 with no given explanation (Wikipedia's explanation that the filming locations no longer existed is not backed up by any source). The show revolves around three high school students who secretly work as spies. The cast changed each few seasons.
Episodes of the show were uploaded to YouTube by a channel called MiHighEpisodes, as well as another channel called mihighseries, including most of the fourth season and the entirety of the fifth season (all but it's finale uploaded by someone else). However, essentially most of Season 1, 2, and parts of 3 were lost due to being taken down or geoblocked, being only accessible to those in the United Kingdom (which would make sense).
The episodes still technically existed in the form of being rerun on several European television networks including SVT and NRK as of late 2018 and as a result being streamable on their websites but are unplayable by those outside of Sweden and Norway (respectively). By using a VPN to access the episodes, it is found that they are dubbed in their respective languages.
Sometime in early 2019 however, torrents surfaced of the entire show in 720p quality, being of remarkably higher quality and most importantly in their entirety.