Thailand’s top court has ruled that former prime minister Thaksin Shinawatra must serve a year in jail, in yet another blow to the influential political dynasty.

The decision relates to a previous case where he was sentenced to years in prison for corruption, but ended up spending less than a day in a jail cell as he was moved to a hospital.

On Tuesday, the Supreme Court ruled that this transfer was unlawful – and that the 76-year-old would have to serve his sentence in prison.

Thaksin and his family have dominated Thai politics since he was first elected PM in 2001. His daughter Paetongtarn previously served as leader but was removed from office last month over a leaked phone call.

Shortly after the ruling was announced, Thaksin released a statement on social media stating that “even though I lose my physical freedom, I will still have freedom of thought for the benefit of my country and its people”.

He also vowed to maintain his strength to serve the monarchy, Thailand and its people.

The former PM was ousted in a military coup in 2006 and spent years living in self-imposed exile, mostly in Dubai.

When he returned to Thailand in 2023, he was promptly tried and found guilty of corruption and abuse of power during his time in office and sentenced to eight years in prison.

But Thaksin spent only hours in a jail cell before he complained of heart issues – and was later moved to a luxury wing of Thailand’s Police General Hospital.

Following his plea for a royal pardon, the Thai king commuted his sentence to one year.

Thaksin stayed in hospital for six months, then received parole and moved to his home in Bangkok.

On Tuesday, a Supreme Court judge said in a statement that Thaksin “knew or could perceive that he was not in a critical or emergency condition”.

While Thaksin had underlying chronic medical conditions, he could have been treated as an outpatient, the judge said while ruling that the hospital stay was illegal.

The “14th floor case”, as it is known in Thailand because of the hospital floor he stayed at, has attracted intense scrutiny.

The handling of the case has led to criticism from many Thais, who say the rich and powerful are often given privileged treatment.

Prior to Tuesday’s ruling many were closely monitoring Thaksin’s movements.

Last week he flew out of Thailand in a private jet to Dubai, where he said he was seeking medical treatment. He said on social media that he intended to fly back for the court hearing.

He showed up in court in Bangkok on Tuesday morning with Paetongtarn, smiling and greeting the media and a group of supporters. Thaksin was wearing a suit with a yellow tie, the colour associated with Thailand’s monarchy.

Paetongtarn told reporters after the ruling that she was “worried” for her father but that he and their family were in “good spirits”.

She also said she would take the family’s Pheu Thai party forward in their work as an opposition party.

Thaksin’s case takes place at a time of political turmoil in Thailand, and Tuesday’s court decision is yet another sign of the changing fortunes of the Shinawatra clan and Pheu Thai.

The “14th floor case” is not the only case Thaksin has faced in recent months.

He was also separately accused of insulting the Thai king, but last month a court acquitted him of lese-majeste.

Meanwhile Paetongtarn was embroiled in controversy after Cambodian leader Hun Sen leaked a phone call he had with her over the Thai-Cambodia border conflict, in which she was heard addressing him as “uncle”.

She was then removed from office after the constitutional court found her to be violating ethical standards expected of her office.

Last week Thailand’s parliament chose Anutin Charnvirakul as the new PM, the third in two years.

Anutin’s Bhumjaithai party broke from the coalition led by Pheu Thai, and secured enough support in parliament from another party to win the premiership.