He said the total loss from the project could reach as much as 466 billion baht.
He based the expected loss figures on rice release information from the Commerce Ministry.
According to the figures, the government has bought 26.75 million tonnes of milled rice during the past two harvest years at an average cost of 28,673 baht per tonne (including handling costs).
The government, through the Commerce Minister, however, has sold 12 million tonnes at an average price of only 10,750 baht per tonne. That has already resulted in a loss of 215 billion baht, he said.
He said the government still has about 14 million tonnes of rice in its stockpile.
"Even if the government is able to sell its remaining stock at the same price of 10,750 baht per tonne, it would still stand to lose another 251 billion baht," MR Pridiyathorn said.
Based on his calculation, the total expected loss over the two years of implementing the programme would amount to 466 billion baht.
"It would be even higher if the government had to settle for lower prices because of deterioration of the stockpiled rice," he said.
Last week, MR Pridiyathorn, also known by his nickname of Mom Oui, gave a press conference in which he called the government's rice-pledging scheme the biggest loss-incurring project ever conceived.
At the time, he estimated that if the government could sell all of the pledged rice stockpiles by 2015, it would make losses of at least 425 billion baht _ 205 billion baht from the 2011/2012 crop and 220 billion from the 2012/2013 crop.
MR Pridiyathorn's comments prompted government ministers to defend the project.
Finance Minister Kittiratt Na-Ranong said MR Pridiyathorn, also a former governor of the Bank of Thailand, does not understand the programme's accounting system.
Deputy Prime Minister Niwatthamrong Boonsongpaisan, who is also commerce minister, said actual losses from the scheme as of January were only about 100 billion baht.
In response to MR Pridiyathorn's latest estimates, Deputy Commerce Minister Yanyong Phuangrach yesterday said it was impossible for the rice scheme to cause as much as 466 billion baht in losses.
He said the government has spent about 600 billion baht on the project. It expected to earn 200 billion baht from rice sales by the end of this year.
"That means there is a gap of 400 billion baht. But we have more than 10 million tonnes of rice in stock. Even if we sell the rice at half price, we would still earn about 200 billion baht," Mr Yanyong insisted.
He added that his calculation means the government will be only about 200 billion baht short, which amounts to a loss of about 100 billion baht a year.
MR Pridiyathorn insisted yesterday that number was impossible based on the rice release information from the ministry itself.
"It's clear the ministry's argument is completely wrong. The issue is whether the ministry understands the issue but conceals the loss figures, or if it does not understand anything," MR Pridiyathorn said.
Despite the anticipated losses, he urged the government to speed up the sale of the stockpiled rice, at any price.
"Now it's time to face the truth and help one another tackle the problem," he said. "The time is also ripe for the government to scrap the scheme, as it is proven that any further moves will lead the government to incur heftier losses," he said.
In an article released yesterday, Thailand Development Research Institute fellows Nipon Puapongsakorn and Kampol Pantakual said the government's loss figure of about 100 billion baht a year differs from MR Pridiyathorn's at more than 200 billion baht a year because they use different methods to estimate the value of the rice in the stockpile.
The government estimates the value of its stockpile at the buying cost of 15,000 baht per tonne. MR Pridiyathorn, however, calculates it based on market prices.
The academics said the mark-to-market valuation method should be the preferred one for this project.
They said the government, through the ministry, could have misled the public into believing the rice-pledging scheme is incurring less of a financial burden than it does in reality.
"Regarding the rice-pledging project, the government must keep its accounts up to date and ensure they reflect the real situation as closely as possible."