A secret court in Uzbekistan is poised to sentence a retired career diplomat to up to 20 years in prison on a treason charge that his family says is the result of repression and a broken justice system.

The trial of Kadyr Yusupov, a former top-ranking official who served in London in the early 2000s, was delayed for months while international observers and foreign journalists descended on Uzbekistan for last Sunday’s parliamentary elections.

After the controversial elections, the court abruptly planned a session for Tuesday afternoon. The court is closed even to Yusupov’s family because the charges concern national security.

“Tomorrow, on the eve of Christmas, the #Uzbek justice system will likely deliver a verdict in my father’s case. The judge chose 24th of December date – complete coincidence or another act of calculated callousness?” his son Temur tweeted on Monday evening.

On Tuesday, Yusupov’s son and daughter waited outside of the courthouse for news on their father’s case. The court later delayed the hearing, rescheduling it for later this week, according to family members citing a lawyer. It was the fifth time that closing arguments have been delayed in Yusupov’s case.

Yusupov’s family have little doubt that the secret court will find him guilty. “We were all kind of waiting for this to happen,” Temur Yusupov said in an interview on Monday. “My father is waiting too.”

In December last year, Yusupov threw himself under a train during an apparent suicide attempt. After being admitted to hospital, he was subjected to hours of questioning by security officials. When Temur arrived at his bedside with medicine, he said, his father made a surprising confession: he had been paid to spy for a foreign government since 2015.

Temur believes his father’s confession was coerced: “He was pressured. I’ve known my father for a long time. I know when he’s OK and when he is not … I talked to him and he wasn’t in his right mind. He was delusional.”

Yusupov also said he had been threatened with torture by security officials, and got threats of rape and torture against his family. The United Nations Committee Against Torture said in a 6 December report that it was “concerned” about the case.

The Uzbek government has boasted of reforms under its new leader, Shavkat Mirziyoyev, but little has changed in the country’s archaic legal system. According to relatives, a lawyer for Yusupov had seen an increase in appeals from potential clients facing “secret” charges amid purges and a bout of score-settling in the country’s government agencies.

Yusupov was the deputy head of mission at the London embassy in the early 2000s, and told his children he was most proud of strengthening relations in the years after the 11 September 2001 attacks.

He also served as a senior diplomatic official in Vienna. He left government service in 2009, and worked in the private sector to encourage foreign investment in Uzbekistan.