|Full Name||Stewart Critchley|
|Relationship||Blane Whittaker (best friend)|
|First Episode||The Sinister Prime Minister|
|Last Episode||Asteroid Attack|
|Portrayed By||Scott Gibbins|
Blane Whittaker is his best friend and side-kick and he believes in UFOs and the supernatural. His favourite TV programme is Star Trek and he also runs the school radio club. Stewart knows nothing about Blane being a spy but Blane has been close to telling him a few times. However, Stewart gets suspicious when Blane keeps disappearing all the time.
Stewart has feelings for Daisy Millar and has been said to have compared her to video game character "Queen Valhalla" in "Nerd Alert", but indicates he also likes Rose Gupta. Stewart has earned his Green Blue Peter Badge and can be seen wearing it on his coat and school uniform.