Jeremy Brown is an agent with MI7.
That is a department inside the British intelligence community and deals with, well, unusual things. I say that because I do not believe it is ever mentioned exactly what its scope of interest is but it has to be pretty wide considering it deals retrieving a valuable satellite (sounds like normal spy stuff) to investigating with the undead in Egypt (definitely not normal) to heading to the planet Mars to battle slimy aliens (absolutely not normal).
One other aspect to MI7 is that is uses kids as its operatives. That's correct. Kids, as in youngsters who are normally in school annoying their teachers. In the case of Brown, the school is Grotside and in that facility Brown is just another student. People at the school do not know he is a government employee.
Brown is described as both "short and scruffy" and "weedy" - not sure what a weedy kid looks like. The description also mentions his wearing glasses but the images showing Brown do not have him wearing frames so who knows. It could be he only needs them to read or perhaps he has contact lens. More likely it is just a disguise so other kids will not suspect his true profession. The 'short' is pretty obvious from those pictures but then again, he is just a young kid. Scruffy? Yeah, that is definitely true.
Oh, one other adjective I have seen used for him on more than one occasion is 'typical' - don't believe it. Typical schoolboys do not receive coded messages in class and have to ask to be excused before heading off to save the country or the planet. Well, I do not think they do.
Brown is the agent of record, so to speak, and is the one getting the limelight, not to mention his name in the title of the adventures. Someone who is being decidedly snubbed there is Patsy Spudd, a curly ginger-haired young girl of the same age as Brown (10-ish?) who is probably best described as his sidekick though I would not do so when she is in hearing range. Brown has learned the hard way that is not a good thing to say so he is pressed often to come up with other ways to explain their relationship so as to not get her angry.
And angry seems to be a normal state for Spudd as she enjoys nothing more than when she is given a chance to either eat or beat up someone. She is pretty darn good at both - regarding the latter she is said to be a "mean lean fighting machine" - note the changing of the order of words in that one.