A 78-year-old Minchinhampton man who was trusted as a "stand in grandparent" allegedly raped a teenaged girl at the end of 2015, a jury was told at Gloucester Crown Court yesterday.

Norman Byron, of Longfords Mill, Minchinhampton, has been declared mentally unfit to plead or stand trial by three psychiatrists, so the jury is being asked to decide if he committed the alleged offences.

Byron is accused of raping a 15-year-old girl between October 31, 2015 and January, 1, 2016.

Mark Worsley, prosecuting, told the jury their job is to be sure that Norman Byron did rape the young girl as alleged.

"The victim alleges this happened in November or December 2015. She is now 17.

"In January last year when she was 15 turning 16, she made a complaint to the police that he had sexually assaulted her. Touching her breasts, and making her put her hand on his private areas.

"She said he was doing it on 'loads' of occasions. At that stage she did not disclose any rape."

Mr Worsley told the jury that her family left for a skiing holiday in February last year and the girl then told her mum that she was 'worried as her period hadn't started.'

"She feared she might be pregnant. Her mother was worried. The girl had previously said the defendant hadn't had sex with her," said Mr Worsley.

"The victim then disclosed he had had sex with her, forcing her into that act. She told her mum, but was too ashamed to tell the police.

"On the February 15 her mum rang the police, and the victim gave a second police interview on February 23. The first having taken place on January 7.

"In the first interview, she said she knew the defendant who was friends with the family. He was like a stand-in grandparent.

"He touched her inappropriately. The defendant groped her breasts, put his hand down the front of her clothes, saying 'that's nice' He touched her on many occasions.

"Every time he was alone, he took his opportunities. He would touch her on top of her clothes, sometimes underneath. He tried to kiss her on the lips.

"He threatened her, told her not to tell. He would shout at her if she didn't co-operate.

"He knew what he was doing was wrong.

"In her second interview she said 'he forced me to have sex, but it didn't last long.' He got on top, he asked her, but she said no. He forced her to have sex for two minutes.

"It hurt her. She pushed him off. He was angry with her. He told her if she told, she would be taken away.”

The trial of issue into whether or not he did the acts alleged continues today.