BANGKOK – Embattled Thai ex-premier Yingluck Shinawatra was in defiant mood on Tuesday as she prepared to give a closing defence at her trial for negligence linked to a rice subsidy policy that could see her jailed.

A crush of supporters at the Supreme Court, many with banners reading "We love Yingluck" and "We’re by your side", mobbed the former prime minister, whose personal appeal among her heartlands has surged as her legal travails have deepened.

Yingluck’s government was toppled by the army in 2014 and then retroactively impeached.

She faces a criminal charge of negligence over a flagship policy of her premiership paying farmers nearly twice the market rate for their crops, pouring billions of dollars on her rural voter base.

But it also allegedly caused massive graft.

The August 25 verdict could see Thailand’s first female prime minister jailed for up to 10 years.

Her trial for the outcome of a policy is unprecedented in Thailand, a febrile kingdom where legal claims and counter claims swirl around most key political players.

"I am ready to give my closing statement. I was not corrupt and I confirm my innocence," she told reporters in brief comments, adding she has "not received justice".

A guilty verdict also incurs an automatic lifetime ban from politics – a potential gut punch to the Shinawatra clan whose candidates have won every Thai general election since 2001.

She has the right to appeal any conviction.

The ruling is being eagerly watched as a test of the kingdom’s stability after a decade defined by coups and bloody street protests.

It is also a bellwether of the resolve of Yingluck’s supporters in the face of a junta which has comfortably corralled them since seizing power in 2014.

"The trial is an injustice, Yingluck did nothing wrong," said 77-year-old farmer Perm Duangchan, who travelled several hours to greet the ex-PM at court.

"I want her to win the case so she can come back and help the country."

In a sign of government concern over potential unrest hundreds of police were at the court on Tuesday as the 18-month trial neared its end.

Yingluck is entangled in several other legal cases including a civil case seeking $1 billion compensation for losses over the rice policy.

The courts threaten checkmate for the close-knit Shinawatra family, whose political networks spread across the north and northeast of the kingdom.

On Wednesday the Supreme Court is due to rule whether Somchai Wongsawat, who was briefly premier in late 2008 and is the brother-in-law of Thaksin Shinawatra, is guilty over a deadly crackdown on a protest.

He also faces jail if convicted.

Billionaire Thaksin sits at the core of Thailand’s festering divide.

He was overthrown as prime minister in a military coup in September 2006 and currently lives in self-imposed exile to avoid jail for graft convictions in Thailand.

He is hated by the arch-royalist army and their supporters among Bangkok’s elite, who for a decade have turned to coups and the courts to regain power after losing elections. – AFP