what constitutes offence

No. A person is not criminally liable for an offence simply because he does an act or omits to do an act as commanded by anybody, including police officers or any government official or powerful person. A person is only criminally liable when the act he does or omits to do is expressly stated, in a written and enacted law as an offence and which the penalty for disobedience is also stated. So, just disagreeing with a police officer, or anybody at all, for that matter, on anything which he does not have the backing of a written law to ask you to do, or not to do, which no written law mandates you to do, or forbids you from doing, in which law what the punishment or penalty for not obeying would be clearly stated, does not constitute an offence. See section 36(12) Constitution of the Federal Republic of Nigeria 1999 (as amended)

Yes. To know those acts and omissions that constitute offences, one must look at the sources of criminal law in Nigeria. Usually, the sources of criminal law in Nigeria are grouped into Primary and Secondary sources. Primary sources are principal enactments without which commencing criminal trial will be impossible. Some sources of criminal law are; Administration of Criminal Justice Act 2015; the Administration of Criminal Justice law of the various states in Nigeria; the Criminal Code Act; the Penal Code Act; Constitution of the Federal Republic of Nigeria 1999; the Economic and Financial Crime Commission Act (applicable nationwide) the Independent Corrupt Practices Act, etc. etc. There are several other pieces of documented and published sources in which acts and omissions are indicated to be offences against the State, and the punishments set down for each of them outside of the list hereinabove. The Rules of Procedure (Criminal Procedure), i.e. the Criminal Procedure Act (CPA for the Federation) and Criminal Procedure Law (CPL for the States) would also help the curious mind to better understand the issues of the nature of offences.

Generally, it is the local Act, laws, rule and practice directions that govern and regulate criminal proceedings in Nigeria. However, where such Acts, laws, rules and directions are silent on any particular matter relating to practice and procedure, the English Rules of Practice and Procedure will be applied to fill that lacuna. See Board of Custom and Excise v Hassan (19758) 2 LRN 56; Simidele v C.O.P (1966) NMLR 116; Ikomi v State (1986) 5 SC 313.