BANGKOK, Jul. 16 (Reuters): Thailand's billionaire former premier Thaksin Shinawatra will hear a verdict on a royal insult case on August 22, his lawyer said on Wednesday, the first in a series of challenges against him and his daughter, Prime Minister Paetongtarn Shinawatra, whose government hangs by a thread.

Although Thaksin has no official role in government, he remains highly influential and is seen as the power behind the ruling Pheu Thai party, now besieged by a faltering economy, a border crisis and uncertainties arising from a slew of other legal challenges.

"We are confident that we will receive justice," his lawyer Winyat Chatmontree told reporters.

Thailand has one of the world's harshest lese-majeste laws, setting jail terms of up to 15 years for anyone convicted of defaming, insulting or threatening King Maha Vajiralongkorn and his close family.

Thaksin faces a separate case over the legitimacy of his prolonged hospitalisation, which could also potentially send him back to jail.

The controversial politician was imprisoned after his dramatic homecoming from self-exile in 2023 to serve a sentence of eight years for abuse of power and conflicts of interest.

The sentence was reduced to one year by the King. During his first night in prison, he was transferred to a police hospital after complaining of chest pains.

Thaksin remained in the hospital's VIP ward for six months until he was released on parole. His prolonged stay has sparked public outrage and raised questions over his ailment.

Thaksin's daughter, Paetongtarn, the country's youngest leader, was suspended from duties in June over a leaked phone call where she appeared to kowtow to Cambodia's former leader Hun Sen and criticised a Thai army commander, triggered a major backlash at home.

Her coalition maintains a razor-thin majority after the exit of its second-largest coalition partner over the same issue, with protesters calling for her resignation.

Photo from Reuters