Singapore's president must remain elected because he has custodial powers over the use of past reserves and a mandate is needed to exercise those powers, Prime Minister Lee Hsien Loong said.

During hearings by a Constitutional Commission on the review of aspects of the presidency in April and May this year, several individuals suggested a return to the system of an appointed president to ensure minority representation.

But this puts the president in a difficult position if he has to go against the wishes of the government of the day to use the nation's reserves, Mr Lee said in a television interview broadcast last night.

In such a situation, the government may well "retort, 'Who are you to say no to me? I have a mandate, I went to election, I published a manifesto and now you're saying I can't spend this money!' "

"That will put the president in a very difficult position," he said. "If you actually have to wield those powers and say no, it will not work. So if you want to have a safeguard, you must have an election."

He noted that some do not see the need for such a safeguard and argue Parliament should decide on everything. Singapore had such a system for its first 25 years, he noted. But most governments ensure powers are divided, for example, by having an Upper House or an elected president with considerable powers.

"You have a balancing system to stabilise the political system to make sure you don't have one mishap and the whole boat flips over," he said. "We need these stabilisers in our system, which is why we created the elected president."

Mr Lee cited the example of Australia to illustrate how without such a safety net, Singapore could have run into difficulty. Australian elections became "auctions" as government and opposition competed to promise ever more benefits and welfare during the commodities boom. Now the boom is over, their Budget is in deficit and there is nothing to give away, he added.

He said: "We have been accumulating reserves over many, many years now and I believe over the last 25 years, if we had not had this elected president, we would have been pushed towards auctions."

Singapore's opposition knows that even if it were elected and wants to spend the reserves, the president can say no, he added.

"Which may well be one of the reasons why the opposition says, 'Do away with the powers and the safeguard'. But I think for Singapore's well-being, we should keep that safeguard," he said.

Asked about the 2011 presidential election with four candidates, Mr Lee said "many of the candidates did not understand or did not accept what the president's duties are, what his constitutional role is and what he's being elected to do".

"They made statements and promises to the voters which are really not the president's responsibility or duty or function," he said.

"There can only be one government and the president has certain roles and duties, which are to hold the second key on money and on people but not to go and check the government or tell the government what it is supposed to do.

"Not all the candidates understood that or maybe they did but they thought if they made these statements, it would help them to win the election," he added.

"That is one of the difficulties of having an election for president and it's a difficulty which we have to find some way to overcome."