THE man on trial accused of murdering Southampton schoolgirl Lucy McHugh could “become angry at the flip of a coin”, the teenager’s grandmother told a court.

Dawn White told jury members she once broke up an argument between Lucy and alleged killer Stephen Nicholson, in which she claimed she saw the 25-year-old swearing at the teenager.

She also told the court that she found a letter, written by Lucy about Nicholson, days before her body was found in a wooded area of Southampton Sports Centre on July 26.

But the family dismissed the letter, which was not read out in court, because they believed the 13-year-old had an “infatuation” with Nicholson.

Mrs White was speaking at Winchester Crown Court on Thursday, during the trial of Nicholson, who denies Lucy’s murder.

He also denies two allegations of sexual activity with a child against Lucy on multiple occasions and denies sexual activity with a child in relation to another girl aged 14.

The court was told how Lucy had moved into her grandparents’ home for six months last year, after a number of arguments with Nicholson, but returned in June.

Mrs White, Lucy’s grandmother on her mother’s side, told the jury she witnessed one argument between Nicholson and the teenager.

She told the court she broke up the argument and demanded Nicholson leave.

Asked by prosecutor William Mousley QC how quickly Nicholson could become angry, she said: “Very quickly. At the flip of a coin.”

Speaking about a letter, found under Lucy’s pillow days before her disappearance, she said: “We all thought Lucy had an infatuation with Stephen.”

She added: “All 13-year-olds have secrets. There are just somethings they won’t tell you about.”

On Thursday, the court also heard from a police analyst and navigation expert, who gave evidence about location data on Nicholson’s phone.

The data showed Nicholson’s phone located at a friend’s home near to the Sports Centre on July 25 – the day Lucy went missing.

It also showed him leaving the area around 11am, before briefly stopping in the Tanners Brook area.

Mr Mousley referred jury members back to his opening, in which he told the court that clothes with blood on - matching Lucy’s DNA - were found nearby.

The trial is set to continue on Monday.