cross boundary enforcement - Public forum - Planning Advisory Service (PAS)

Hi,  we have an unauthorised change of use of land mostly in our district but a small part in the neighbouring district.   A retrospective application was received and dealt with by this authority as the largest area.  The application has been refused, a decision supported by the neighbouring authority.   We now want to take enforcement action but can one authority serve the notice covering the neighbouring land as well or do we each have to take action for our respective areas ?