Sergeant Richard Evans, 46, allegedly had sex with the mother-of-three while on duty at Ystrad Mynach police station.
The court heard that Evans had sex with her up against a sink in a sluice room at the police station the morning after her arrest while drunk.
The woman said: “I just let it happen, I wanted it to happen. It was flattering – you’ve got a man in uniform and he fancies you.
“I felt a bit cocky – not everyone can say they’ve had an affair with a policeman.”
The woman was taken to Ystrad Mynach police station in May 2006 when she was “worse for drink”.
She was “extremely” thirsty the next morning and asked Evans for a drink of water.
He allegedly took her into the sluice room, before shutting the door and having unprotected sex with her.
The woman said: “He put his arms around my waist and started kissing the back of my neck.
“Then he was undoing my jeans and pulling them down, and then my underwear, and we had sex.”
She added: “He said nothing to me afterwards, like it was one of those things that had happened, but ‘so what?’
“There was no feeling. It was just a quick bunk up and be done with it – there was no love.
“It was a giggle, it had been exciting.
“That’s all it had been – it was no strings and no feelings, just sex.
“It wasn’t promises and chocolates, it was just a five minute fumble.”
The woman told the court how she first met Evans in 2003 when he gave her a lift back home.
He allegedly took her into the back of a police van before kissing her and touching her breast.
The woman, who cannot be named for legal reasons, did not report either incident and they only came out when Evans was investigated for allegedly sexually assaulting two other women.
Evans is accused of touching another woman’s breasts and kissing her while she was being kept in custody at the police station.
He allegedly watched another woman getting changed before pulling off a blanket she had wrapped around herself to stop him seeing her breasts.
Prosecutor John Philpotts said: “While acting in the capacity of a custody sergeant, he engaged in sexual activity with three females who were in his care.
“He also gave one of these females a lift in a police vehicle and on that occasion he touched her sexually.
“If a police officer engages in sexual activity with a member of the public who is in his care then that constitutes misconduct.”
Evans, of New Inn, Pontypool, Gwent, denies misconduct in a public office and three charges of sexual assault.
The trial continues.