The director of a school accused of demanding 400,000 baht in "tea money" from a parent in exchange for enrolling a student has denied the allegation, claiming he is the victim of a plot to oust him by disgruntled alumni whose children were not admitted to the school.

Samsenwittayalai School director Viroj Samluan described it as a "well-organised plot".

The case first drew the attention of the media after one parent circulated a video clip allegedly showing the school director receiving money for accepting his child into Mathayom 1 (7th Grade).

Samsenwittayalai School director Viroj Samluan appears Tuesday at a news briefing. (Photo by Wichan Charoenkiatpakul)

The clip showed a parent, whose name has not been disclosed, placing a brown envelope filled with cash on a table in what was claimed to be Mr Viroj's office.

The parent allegedly recorded every contact with the school director, including phone calls and the handover of the purported bribe. The director was said to have had his deputy accept the cash on his behalf.

The parent said the cash was a bribe and that the video footage was made public to get the permanent secretary for education to look into the issue.

At a press conference Tuesday, Mr Viroj insisted he had never sold enrollments.

He said the student in question was admitted on April 5 while the video showing the alleged "tea money" was shot two weeks later on April 19.

The student was one of sixty who enrolled in Mathayom 1 this year under special conditions made available to the school's land donors, benefactors, the children of teachers and students from partner schools. Other students had to pass a rigorous test.

"If the student had already been admitted, there was no need to pay any tea money. Moreover, why was the clip not circulated immediately ... but rather delayed until June?" Mr Viroj asked.

He said he believes he may be the victim of a conspiracy by a group of school alumni who were upset their children could not get into the school.

He said these alumni had requested the school secure seats for their children in Mathayom 1 and Mathayom 4 (Grade 10) every year, but that the school could not "help" all of the students.

He said the video was a "set-up" aimed at blackmailing him into compliance.

Also Tuesday, Mr Viroj lodged a complaint with Bang Sue police station, filing a defamation suit against the parent who released the clip.

"Under school regulations, parents cannot donate money before the announcement of the entrance exam results, and every time the school receives a donation we must give donors a receipt as a record -- so the bribe never took place," he said.

In a statement, Samsenwittayalai Alumni Association said the scandal has hurt the school's reputation. It urged the Education Ministry to investigate the issue.

On Monday, the Office of the Basic Education Commission (Obec) set up a fact-finding panel and sent its legal experts to look into the case.

Obec secretary-general Karun Sakulpradit said the director will be transferred and face disciplinary action if the allegations are confirmed.

Prime Minister Prayut Chan-o-cha said he ordered the Education Ministry to clear the matter up. "I insist we should not have any more 'tea money' incidents," he said. "More importantly, we have to ensure all schools have the same standards."