The court heard that Khan became physically and verbally abusive after having known the woman for about a year.
After he tried to have sex with her at the picnic, she ran away but Khan caught her then raped her.
Senior investigator Kath Blain, from the NCA’s Operation Stovewood, said: “When the victim first met Khan he showed no signs of being violent, however after gaining the woman’s trust Khan became abusive and that behaviour quickly escalated to sexual violence.”
The NCA began an investigation in 2022 after it identified the woman was a victim of rape in the course of separate inquiries.
Khan was charged in February 2024 and sentenced on the same day he was found guilty.
Ms Blain said: “Our evidence and the victim’s brave testimony has resulted in Khan being convicted more than 20 years after he committed his crime.”
She added: “I urge anyone who has been raped or sexually abused, at any time in their life, to report it to the police, who are ready and waiting to help.”