If the People's Action Party (PAP) gets a clear mandate at this election, its mind could change anytime and so could policies, said Workers' Party (WP) chief Low Thia Khiang, as he raised the spectre of a goods and services tax (GST) increase after the polls.

He claimed that the ruling party had said during the 2006 General Election that it was not considering a GST rise. However, it rose to its current rate of 7 per cent in July 2007 one year later.

Mr Low said when then-Senior Minister Goh Chok Tong was asked about the GST hike, he responded that the PAP would introduce unpopular policies after elections as this was politics.

"During the election, the PAP is as tame as a cat. But once it's over, it becomes a lion with its mouth wide open," said Mr Low in Mandarin, at last night's rally for Nee Soon GRC held at Yishun Stadium.

"When PAP gets an overwhelming majority of seats, it will take it that you agree with its actions. After the 2011 elections, the PAP didn't raise the GST. After this election, I'm not sure."

The PAP's vote share slid from 66.6 per cent at the 2006 election to 60.1 per cent at the 2011 polls, where the WP scored a historic win in Aljunied GRC.

Since then, the Government has increased the supply of public housing and introduced measures to reduce property prices, among other policy changes, said Mr Low. But changes for the better can be reversed if the PAP senses that voters are giving it free rein, he added.

"The results and your life after the election is linked. Will your burden get heavier after the polls? You have to think about that," he said.

In an earlier speech, Hougang MP Png Eng Huat said there was nothing to fear about life if the PAP were not in power because the civil service would keep things going.

He said a Thai friend had told him that in the wake of a military coup last year, Thailand was still functioning because of its civil service.

"Likewise, we have a good civil service in Singapore, but the PAP wants to frighten you," he said.

Mr Png added that Deputy Prime Minister Teo Chee Hean had cautioned against "revolving-door politics", where a country's government changes with every election.

"Well I would like to assure the DPM if PAP loses power one day, he can go home and take a hot bath because water will still be running. He can read the newspaper and surf the Internet because electricity will still be running," he said.

He said voters in the WP-held constituencies of Aljunied GRC, Hougang and Punggol East Single-Member Constituencies should get the credit for policy improvements.

"Because it gave the PAP seven tight slaps, that made the difference. Imagine what 28 slaps can do," he said, referring to the seven elected WP MPs and the total number of seats the party is contesting at this polls respectively.

It was a point also made by party chairman Sylvia Lim, who delivered the last speech of the night.

"The PAP has been trying during this election to convince you that many changes we see around us started before 2011. They are afraid that the WP will take credit for the changes. But we are not taking credit. The credit belongs to you, the voters," she said.

Ms Lim cited the added investment in public transport infrastructure, increased supply of new HDB flats, and the tightening of foreign manpower influx as examples of the PAP correcting its past errors.

"Your votes forced the PAP to wake up and do something about their big mistakes in policy and planning," she said.

• Additional reporting by Amir Hussain