A teenager has been found not guilty of raping his step-sister.

Jurors took around two-and-a-half hours to acquit the man, who we are not naming in order to protect the identity of his step-sister, on allegations of rape and sexual assault by penetration.

It followed a week-long trial at Swindon Crown Court, during which the 12-strong jury heard competing accounts of what happened on a night in late 2018 when the defendant and his 15-year-old step-sister were home alone in Swindon.

The defendant, who had no previous convictions, admitted to having had sex with the girl, but claimed he had been able to tell “from her body language” that she was consenting to him first touching her sexually then having penetrative sex on the sofa as they watched 80s film The Breakfast Club. 

Under cross-examination, the man’s alleged victim said repeatedly that she had not consented to having sex and had tried to push her step-brother’s hand away as he touched her leg. “I told him to stop, then I got very anxious and I froze,” she said.

The allegations came to light early last year after the girl’s mum was sent a Facebook message by her daughter’s friend. The defendant was challenged by his dad and step-mother and had to go and live with his mother. He had dropped out of college.

Closing the case for the defence on Monday, barrister Sam Parham said: “Of course, having sex with a step-sister is very unusual, some people might say messed-up. It crosses a line that step-siblings don’t usually cross. It’s unacceptable in this case, of course, because the complainant was under 16 at the time.

“It’s had the effect of completely splitting up her family unit. It’s had tragic consequences, really, and I don’t use the words lightly, for a number of different people who were involved.

“This case is not about underage sex inside a family, however serious that is. This case is about something altogether more serious than that: forced sex without consent of a girl who was underage at the time.

“It’s clearly an unusual case. The stakes for the defendant couldn’t be higher.”

In her opening speech last week, prosecutor Mary Aspinall-Miles said: “The prosecution case is very straightforward. They’d never been left alone together before like that and for whatever reason – and the prosecution don’t have to prove why – this defendant used the absence of the parents and the complainant’s isolation to rape her and to take advantage of her.”

The crown court trial was the first to be partly heard in the cavernous courtroom two at Swindon Magistrates’ Court, with social distancing measures that included clear plastic screens put up in front of some jurors. There are not enough courtrooms in the main crown court building to run two jury trials simultaneously while abiding by social distancing rules.