Section 154 of the code of criminal procedure (crpc) enunciates that the police officer will reduce the oral information in writing. Therefore, he has no power to demand from the informant to give the information in writing. The crpc was first enacted in 1882 and the very first version; it devised the procedure for lodging of First Information Report (FIR). At that time, the literacy rate was too low, and it was the duty of the police officer to itself record all information in writing.
The same procedure is prevailing today, and officer in charge of the police station cannot insist on providing information in writing. However, the FIR is not a piece of evidence, and it has a minimal purpose. The primary objective is to receive the information as early as possible. Hence, the very first information about the offence is called the FIR.
Written information is not mandatory
In State of Haryana vs Bhajan Lal AIR 1992 SC 604, the Supreme Court has held that the information must disclose the commission of a cognizable offence. The police office upon receiving such information he has no option except to record the FIR and launch the investigation.
In all cases, the investigation starts instantly after the recording of the FIR. If the police investigate the matter without registration of FIR, such investigation is disastrous in the eye of law. Though, in very exceptional cases, the police can investigate the case after making an entry in the general diary.
There is no provision in the code of criminal procedure which mandates that the police will register the FIR only on the receiving of written information. Hence, the act of that police officer is forbidden, and you can file a complaint before the Superintendent of police to take proper action against him.