Orangeanddemons that may be what your school tells you, but my DCs school does deal with bullying outside of school, patrols bus stops etc., and deals with issues such as cyber bullying.
If someone brings shame on the Uniform, which means it both has to be identifiable as a particular school's uniform, as well as missworn, is punishable by detentions etc. as for in school crimes. Bad behaviour outside school is dealt with by assemblies, but may also bring police involvement if necessary.
Of course I'd known few students actually be punished for incorrect wearing of ties or rolled up skirts, outside of school - but they are all informed it could happen when they start (and teachers do take on duties of patrolling bus stops after school).