A Bristol juror listening to a sex case went out at lunchtime and carried out a sexual assault himself, a court heard.

Bristol Crown Court heard former soldier Alan Edwards had a history of mental health problems and had got himself excused from hearing a child abuse trial, only to be called instead to serve as a juror in the case of a sex assault on a teenage girl.

On the third day of the case, while suffering from delusions of persecution, he went to a city law firm's office and molested the receptionist.

Edwards, aged 58, of the Portway, Shirehampton, pleaded not guilty by reason of insanity to a sexual assault charge.

A jury of seven men and five women yesterday found that he had carried out the attack but because of his mental state he was not in control of his actions at the time.

They returned a unanimous not guilty verdict but Edwards will still face a sentence, with Judge Simon Darwall-Smith adjourning the case for reports and telling Edwards he must register as a sex offender.

Edwards' victim told the jury a man arrived at her premises on the day of the assault in July last year and she thought he seemed to be acting oddly.

She told the jury: "I said 'how can I help you?' and he looked at me and said: 'Well, I've had a bad day'.

The woman described how the man sat on her desk and started reading company faxes, which she took from him, then he grabbed her hands and pulled her towards him before nuzzling his face in her neck and indecently assaulting her.

She said: "I started shouting 'No, No, Get off!' but he wasn't listening to anything I was saying. He was making groaning noises like he was enjoying what he was doing."

The court heard that, very quickly, office staff and clients arrived at the scene and pulled the man away.

Edwards identified himself to police who arrived at the scene, the court heard, but struggled and squealed during his arrest and had to be put in handcuffs and leg restraints and carried to a police van.

He told police he felt as if he had been forced to do something against his will, the court heard.

Rebecca Bradberry, defending, read a report by consultant psychiatrist Dr Caroline Bradley who noted Edwards suffered a head injury in a road accident in 1975, while in the army.

He was treated in a military hospital in 1993, then aged 42, after suffering a psychotic episode for which he was successfully medicated.

The court heard Edwards had previously served as a juror in a paedophilia case which had caused him anxiety and odd behaviour, and he had also not been himself after the latest incident.

Dr Bradley said Edwards told her that during his last jury duty he had received a 1am phone call and felt someone was trying to get to him.

On the third day, at lunchtime, he thought he was going to be kidnapped and he walked to the law firm, sat down, put his head back and closed his eyes.

He said the next thing he remembered was being restrained on the floor and he had no memory of any offence. Dr Bradley concluded Edwards was suffering psychotic symptoms, had feelings of being controlled and believed people were out to get him.

She said: "He could not know or control the nature or quality of his actions."

Dr Bradley's conclusion was backed up by consultant forensic psychiatrist Dr Tim Amos.

Edwards will be sentenced next month.