A general election will be delayed for about three months if a referendum is to be held on the draft charter.
However, the government and charter drafters are not yet on the same page where the referendum is concerned.
Constitution Drafting Committee (CDC) chairman Borwornsak Uwanno said Wednesday the charter drafters and National Reform Council (NRC) are not authorised to decide whether the referendum should be held.
The final say rests with the National Council for Peace and Order (NCPO) and the cabinet, he said.
But NCPO chief and Prime Minister Prayut Chan-o-cha said it is the CDC and NRC's job to decide.
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"The cabinet and the NCPO are not authorised to order the referendum," Gen Prayut said Wednesday.
If the CDC or the NRC decide a referendum is needed, they will have to propose it to the NCPO which will pass the proposal on to the National Legislative Assembly to initiate a process to amend the interim charter to allow the referendum to take place, he said.
According to Gen Prayut, the CDC and NRC will have to take responsibility for their decisions regarding the draft charter.
The NRC consists of various groups with different interests and they will have to work it out among themselves, Gen Prayut said.
If there is a referendum, Mr Borwornsak said, the poll will be put off at least until May next year.
But if the draft charter is ready within its stipulated time frame, the general election will take place in late February next year.
Mr Borwornsak echoed Gen Prayut's remark that the interim charter will need to be amended if a referendum is to be held. He said the amendments must be made before Aug 6 - the day the NRC is scheduled to vote on the draft charter.
If the NRC approves the draft, it is required to forward it for royal endorsement by Sept 4.
According to Mr Borwornsak, the CDC has about 40 days to deliberate recommendations put forward by concerned parties and make changes. The last day of the CDC deliberation is July 23.
Gen Prayut clarified Mr Borwornsak's earlier remark that the new charter should be used for five years before any amendments should be considered.
The prime minister said the CDC could have meant that a five-year period is needed for the proposed reforms to take root.
He said the draft charter is not an ordinary version and is designed to address all sorts of problems, especially transparency, accountability and how politicians come to power.
"This charter has to be extraordinary if we want reforms to happen. Reforms can't take place if we use an ordinary charter. How many governments have tried to implement reforms?
"If we don't want reforms, we can write it the way we did before. Actually, we don't need to write a new one at all. If you want the same old troubles, suit yourself," he said.
Asked about criticism that the draft charter - which contains 315 sections - is probably too long, he said something needs to change when it comes to law-making. He said Thai people want laws, but stop short when it comes to enforcing them.
Defence Minister Prawit Wongsuwan said everything will proceed as prescribed in the interim charter.
"If the draft constitution is rejected, things will proceed as prescribed in the interim charter," he said.
Gen Prawit insisted the NCPO has no intention of prolonging its stay in power, when asked about Mr Borwornsak's remark about the five-year enforcement.
He said the NCPO and the government understand the importance of reforms.
Deputy Prime Minister Wissanu Krea-gnam said the government will review the draft charter on May 19 at a cabinet meeting. It will then send its comments to the CDC before May 25.
He said that some aspects of the current draft may limit the efficiency of everyday governance and should be reviewed by officials.
Too much attention is being paid to the political aspects of the charter, such as the origin of the prime minister or senators, as well as the creation of new civic bodies, Mr Wissanu said.
"Ministries should examine proposals which could pose limitations on their work in the future," he said.
Each ministry is expected to submit its comments on the draft to Mr Wissanu by May 14.
The deputy premier, in charge of legal affairs, will then assemble these views and forward them to the CDC.