Prime Minister Prayut Chan-o-cha has slammed the media for failing to move beyond former premiers Thaksin Shinawatra and his sister Yingluck. (Bangkok Post file photo)

Prime Minister Prayut Chan-o-cha has slammed the media for failing to move beyond former premiers Thaksin Shinawatra and his sister Yingluck after poll results showed the public had more confidence in ex-telecoms tycoon Thaksin than it does in the 2014 coup leader.

Both former leaders were ousted from power and replaced by coup leaders. Ms Yingluck is believed to have fled the country last month shortly before a Supreme Court ruling on Aug 25 in her criminal negligence case over her administration's failed rice-pledging scheme.

Gen Prayut responded emotionally to questions from the media on Wednesday about the poll results released by King Prajadhipok's Institute. They showed Thaksin, who was ousted from power in 2006, ranks as the most popular prime minister over the past 15 years.

The survey of 33,420 people was conducted nationwide from April 24 to May 15 to mark the 19th anniversary of the institute. It was done in collaboration with the Ministry of Digital Economy and Society and the National Statistical Office.

Respondents were asked to indicate their confidence in government leaders from 2002 and 2017.

Thaksin topped the vote with an approval rating of 93% in 2003 but this dropped to 77.2% in 2006.

Gen Prayut was No 2 with 87.5% approval in 2015, a year after he staged the latest coup. Public confidence in him declined to 84.6% in 2016.

Ms Yingluck was next with ratings of 69.9% in 2013 and 63.4% in 2014.

Somchai Wongsawat received the worst score of 37.6% and Abhisit Vejjajiva never won an approval rating above 61.6%, the poll showed.

Gen Prayut blamed the media's obsession with Thaksin for Thai politics not being able to lay his memory to rest, even though many critics claim he still pulls the strings for the Pheu Thai Party from behind the scenes. Thaksin is believed to be living in self-exile in Dubai.

"I put him behind me a long time ago but many members of the media haven't and they still run stories about him daily," Gen Prayut said. "I now focus on the law. The way to move past him is to forget him and let the law take its course.

"Otherwise we won't be able to get anything done and the country cannot move forward," he said.

Asked about Ms Yingluck's escape, Gen Prayut said: "It's you [the media] that cannot move past her ... I move past anyone who is at the centre of conflict.

"The media should pose questions that are more useful. The media never asked if I was tired when I attended the Brics summit in China or how much recognition Thailand has gained. The media has never been interested in this," Gen Prayut said.

Meanwhile, Mr Abhisit, the Democrat Party leader, shrugged off the poll results and suggested his party, the country's oldest, was suffering a popularity crisis.

He said the poll results were likely influenced by the current political environment under which the public lacks confidence in political entities.

Parties must work to restore the public's faith, he said. The situation will improve when the current ban on political gatherings and the regulations limiting parties' activities are lifted, he added.

Based on the poll results, the Democrat Party was the least popular party in power with a 36.8% rating.

Also scoring among the lowest were non-governmental organisations (38.3%), the Pheu Thai Party (39.4%), political parties as a whole (43.5%) and the Committee for National Administration under the Framework of National Reform, Strategy and Reconciliation (47.6%).

Mr Abhisit said parties should make use of the current break to make changes and be more transparent.

"If corruption remains unresolved, we don't think other problems will go away. Parties and politicians will have to prove their transparency," he said.

Democrat deputy leader Sathit Pitutecha also played down the results of the KPI poll, saying the public still does not grasp the role the party plays.

He said that parties are not allowed to conduct political activities so their comments or suggestions are regarded as unwanted.

He said their popularity is waning because their roles are limited.

"The problem is the people don't quite understand the structure. Public confidence usually peaks when [parties] are in power no matter where they are from -- elections or a coup," he said.

He said Thaksin and Gen Prayut received high ratings because both men demonstrated strong leadership despite corruption problems.

According to Mr Sathit, public confidence will remain high as long as there is no political upheaval.

Amnuay Khlangpha, a former Lop Buri MP from the Pheu Thai Party, said it came as no surprise when the poll results showed Thaksin was the most popular leader in recent history.

Thaksin initiated policies and measures that responded to the needs of the public, such as the 30-baht-universal health care scheme, and village funds, Mr Amnuay said.

Regarding progress in locating Ms Yingluck, national police chief Chakthip Chaijinday said police and security agencies are investigating which route she may have used and whether she was aided by foreign forces.

National Council for Peace and Order spokesman Winthai Suvaree said police have not sent any information regarding her flights to the NCPO's legal team.

Deputy national police chief Srivara Ransibrahmanakul said earlier that investigators have given information involving those who helped Ms Yingluck flee the country to the military.

She is believed to have transited via Cambodia and Singapore to Dubai.