You need to complain to the Standards Board for England, (http://www.standardsforengland.gov.uk) and specify which parts of the Code of Conduct were broken (Symbols for stealing campaign materials; Campaign Management Section C for preventing the distribution of another party's leaflets).

I'm not sure what this penalty is, but I know that reps can be banned for up to five years for breaking the CoC.

Let me know what they say!