Former NSW Premier Nathan Rees faces criticism over admitted sex-for-benefit scandal with a constituent.

They had sex in Mr Ree's office; they had met at nights in local parks, including Girraween Park in Sydney electorate of Toongabbie; and they also hooked up after drinks at a local pub, a report from The Daily Telegraph revealed.

A seemingly usual illicit affair, but for the woman involved (identity withheld), it was about seeking Mr Rees' help on a police matter. This issue involved a purportedly act of neglect by police officers to arrest her son's attacker.

At some point in their five-month correspondence and rendezvous, the woman pestered Mr Rees whether he was going to help her with her complaint against the police or whether Mr Rees was only using her for sex.

Consequently, the woman seemed to have found the answer right after, when Mr Rees ended the relationship abruptly without any update about the police matter. After that, she allegedly sent threat messages to Mr Rees; however, she now denies that she sent those threats.

The supposedly beneficial affair started when the two met at a community gathering, back in 2009. She approached him and expressed her gratitude for his staff's assistance with the public housing, The Daily Telegraph reported.

Mr Rees got her phone number from his staff and soon started texting her. Their exchange of text messages had led to at least three sexual encounters, with the woman constantly lobbying him to help her with her police complaint.

As for Mr Rees' part, he did write a letter marked "draft" to the Police Integrity Commission and the Ombudsman in his effort to help her. He gave specific instructions to the woman's lawyer not to send the letter until the woman told her so.

Mr Rees, now opposition police spokesman, said he did not take advantage of his position for the sexual encounters to last longer than it took. He said that the relationship did not even compromise his job.

"This is a private and sensitive matter. I deeply regret my actions and the pain I have caused my loved ones, friends and family. I offer no excuses. At no stage was I compromised in the performance of my duties. For the sake of others, I ask for privacy at this time. I do not propose to make any further comment," Mr Rees announced with regret.