The conference was attended by party executives and Thai and foreign media.
When Mr Abhisit went on stage at around 1.30pm, a man who was sitting in the middle of the room stood up and blew the whistle loudly.
No one tried to stop him as most people in the room thought he was a supporter of the anti-government People’s Democratic Reform Committee (PDRC).
But the man turned to Mr Abhisit and held up a paper with the word “RESPECT MY VOTE” and shouted “If you still cannot reform yourself, how can you reform the country.”
Mr Abhisit appeared to be stunned and tried to control the situation by saying “thank you”.
The man continued to shout, saying, “When you were the government, why didn’t you do it. You should stop the lie. You can threaten others but others cannot threaten you, can’t they?”
Mr Abhisit replied that “This is the example that needs reform. This is the pattern of the competitor of the Democrat Party.” The man replied that “I am not the competitor, I am the people.”
The man was removed by party staff.
“This shows that people can express opinion at one of our activities," Mr Abhisit said. "But there is always some disturbance at our forums. This is the reason why we cannot say that the election will be fair. What is happening is not the right set up.”
The former premier carried with the press conference that focused on the eradiation of corruption which the Democrats view as the origin of all problems in Thailand.
He said damage from corruption each year was high at 300 billion baht, or almost 2% of the country’s gross domestic product, an amount that is sufficient to hire 1.5 million teachers or build 5,000 new large schools or other infrastructure.