THE NSW Ombudsman will investigate claims Rose Bay police deleted sections of CCTV footage crucial to allegations they assaulted a gay man.

David Rook and his partner, John Tanner, went to the police station to report an alleged assault by security guards at the Opera House on June 5 last year.

Scene of the alleged assault ... Rose Bay police station.

But police charged Mr Rook with drink driving and allegedly assaulted Mr Tanner.

The couple applied under freedom-of-information laws for a copy of the CCTV footage but police denied the request citing ''overriding public interest''.