The sister of jailed teacher Jeremy Forrest has promised to support her brother’s relationship with the girl he abducted, and revealed that the girl has allegedly been granted permission to visit him in prison.

Speaking to the Mail on Sunday, Carrie Hanspaul, 33, said: “The girl’s been told that she can visit him. She’s planning on doing that as soon as she can. Jeremy told me that he’d been told that she wanted to visit. In court on the day of his conviction, he said to me, ‘Tell her she’s allowed to visit,’ and when I did she just smiled.”

Mrs Hanspaul also alleges Forrest told his family during a prison visit that he loved the girl and wanted to marry her.

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The girl, who cannot be named for legal reasons, has since apologised for the upset the couple have caused in a letter addressed to Forrest’s parents, but remained resolute that she would wait for the former maths teacher to be released from prison to start a life with him.

The girl reportedly used the letter to establish contact with Forrest’s parents as he awaited trial for child abduction. According to the Mail on Sunday, the girl’s letter stated: “I can’t emphasise enough how everything I feel towards Jeremy is - more than anything – serious… he is wonderful”.

She also mentioned the A-level maths course she will shortly begin, which she said Forrest may find “comical” as “maths was my worst subject at school”.

“Obviously I now and will continue in the future to stand by him. I do believe that some things are worth fighting for”, the letter continued. “For now, though I’m going to concentrate on working hard to get the future both me and Jeremy want and I’m preparing for college.”

Forrest, 30, was jailed for five and a half years for child abduction and five charges of sexual activity with a child. During the eight-day trial at Lewes Crown Court the jury heard that Forrest groomed the schoolgirl into having sex with him shortly after her 15th birthday. The couple exchanged indecent images and were seen holding hands on a school trip.

When police began to make inquiries seven months after initial concerns were raised, Forrest abducted the child and escaped to France, sparking a major man hunt. He spent seven days on the run with the girl but was eventually discovered after trying to secure employment in a bar in Bordeaux. It is understood that Forrest had intended to argue that as the age of consent in France is 15, he had not committed a crime.

In the interview, Mrs Hanspaul said their family would support the girl and “welcome her into the family” if her and Forrest do continue the relationship. She said: “If they’re going to carry on and be in a relationship, we would welcome her into our family and offer any support she was to ask for. We are concentrating on getting him through this.

“He [Forrest] told my dad the first time he saw him that we didn’t need to worry about him, that he was happier now than he’d felt for a couple of years and he could definitely see light at the end of the tunnel. My dad says we are the ones holding that light for him at the end of the tunnel, and if that means supporting the girl then we will do that. He’s asked us to look after her.”

She said she did not see Forrest’s actions as “predatory or grooming”, and compared the age gap to two partners who are 30 and 45, arguing: “‘It’s not going to be a normal relationship as he’s in prison and she isn’t, so they’re not going to be going out or anything. Throughout this we’ve really tried to support him and not to judge him.”

Mrs Hanspaul also revealed that she had spoken to the girl, who she felt “protective of” and comforted her during the trial, at Forrest’s request. “Jeremy mouthed to me, “look after her, comfort her”, because she was really upset. So I just turned around and told her it was OK and put an arm round her. […] I suppose I instantly felt protective. I didn’t want to see her sitting there crying.”

Judge Michael Lawson QC sentenced Forrest to four and a half years for the five offences of sexual activity with a child and one year for the offence of child abduction, to run consecutively.

He also imposed a Sexual Offences Prevention Order (Sopo) on Forrest, banning him from ever working or volunteering with children and unsupervised contact with children, and he was ordered to sign on the sex offenders register.