After a recent push to legalise cannabis in Canberra, police have warned they would have no choice but to enforce federal laws, meaning more people may end up imprisoned.

Chief Police Officer Ray Johnson said the width of ACT offences would remove access to the existing diversion framework, resulting in Federal criminal offences becoming the preeminent charge by default.

As laws currently stand, police have the ability to give users a fine under ACT law, or up to two years' prison under the Commonwealth.