The prospect of fourth election in two years was one of the key talking points to emerge after Mr Michael Palmer's shock resignation on Wednesday.

Asked about it at the press conference, Deputy Prime Minister Teo Chee Hean said it would be a matter that is left up to Prime Minister Lee Hsien Loong.

"Whether there will be a by-election and if so, when is a matter for the PM to decide," he said.

The episode does bear some parallel to events that triggered the by-election in Hougang earlier this year. In that case, Worker's Party MP for Hougang Yaw Shin Leong was expelled from the party after it emerged that he had an extra-marital affair.

Like Hougang, Punggol East is a single seat constituency.

Other questions to emerge at the press conference was the duration of the extra-marital affair Mr Palmer had with the People's Association staff member and how the PA was reacting to the revelation.

While neither DPM Teo or Mr Palmer wanted to delve into the details of the affair, DPM Teo did reveal that the PA staff member has also resigned.

"What the staff member did was wrong. The staff member has tendered her resignation and this is being accepted by PA. PA expects its staff members to maintain higher standards of behaviour and conduct and in this case, the staff member had fallen short."