Answer:
Depending on what exactly you are charged with it can possibly go up to the maximum (UK) limit of ten years but that would mean you've absolutely battered it beyond reasonable possibility..
Usual prison terms can be between a few (2-4) months and 3years, with the higher end being reserved mostly for groups of people attached to a Conspiracy to Commit Criminal Damage charge too, which easily warrants (in the courts eyes) a high custody term.
a better question would be; How do I not get caught? :p
BLERONE PSA...BIRMINGHAM!