A British woman jailed in Egypt for possessing controlled drugs has been refused permission to appeal against her conviction.

Laura Plummer was sentenced to three years in prison for bringing 290 tramadol tablets into the country. She had told the court they were for her partner’s back pain.

Plummer’s lawyer, Mohamed Osman, told the Guardian on Monday: “The court of cassation found there was no mistake in the judgment and refused the appeal.”

Osman declined to say on what grounds he had challenged Plummer’s sentence. He said many factors had gone into the appeal, including the manner in which the initial hearing was handled, but the overall reason was “a long story”.

Plummer was jailed for drug possession by a court in the Red Sea town of Hurghada on 26 December 2017. The 34-year-old retail worker, from Hull, was arrested on arrival at Hurghada airport last October, after a routine scan of her bags revealed that she was carrying a large quantity of the opioid painkiller.

Her family has long maintained she was unaware tramadol is illegal in the country, and that she had brought the pills to give to her partnerafter he injured his back in a car accident.

Plummer initially faced the more serious charge of drug trafficking, which carries a sentence of up to 25 years in prison, or the death penalty for those convicted in Egypt. Problems with translation initially led the retail worker to mistakenly plead guilty to the charge of trafficking.

“The judgment is now final,” Osman said. “This means three years in jail.” Cases similar to Plummer’s usually required the defendant to serve at least half the sentence, he said, meaning that Plummer would spend at least a further nine months in al-Qanater women’s prison, south of Cairo.

Karl Turner, the Labour MP for the Plummers’ Hull East constituency, said: “I’ve spoken to Laura’s father, Neville Plummer. He informs me that Laura’s mother and sister saw [her] on Sunday, and she was told then that the appeal had not been successful. This is obviously disappointing for Laura and the family.”

An estimated 319,000 British tourists visited Egypt in 2017, according to the Foreign and Commonwealth Office, which warns travellers against possession and the trafficking of illegal substances.

A spokesperson for the Foreign Office said its staff “continue to do all they can to support Laura and her family, and our embassy remains in regular contact with the Egyptian authorities”.