a little question

hey guys im a photo and digital specialist workin in snappy snaps at the moment but ive got high hopes on starting some work on the side for the mean time and slowly but surely going to start up my own wee shop on graphics design photo restoring etc but for the mean time if i was to just do small jobs working for clients would i have to register this as a second job and get taxed on it of can i just do it on the side without getting the middle men involved? and would this be legal? i just want to do it by the books! thanks fr the help lads and gals!