The leading minister in Jurong GRC, Mr Lim Boon Heng, told The Straits Times that under the Constitution, no by-election is mandated. The remaining five MPs in the GRC will work out how to share the responsibilities of Dr Ong's Bukit Batok division, he said.

Mr Lim's interpretation of the law is in line with the views of constitutional law expert Kevin Tan, who explained:

'There is no rule to say you need to have a by-election. If you look at previous cases, they don't hold by-elections so long as the constituents are represented.'

He added that there could be a caretaker MP. In the case of a GRC, 'the team will share the workload'.

There have been precedents of seats left unfilled.

When senior minister of state for education Tay Eng Soon died in August 1993, then-prime minister Goh Chok Tong decided against any by-election to fill the seat in Eunos GRC.

Instead, other Eunos GRC MPs - Mr Charles Chong, Mr Chew Heng Ching and Mr Sidek Saniff - took care of Dr Tay's residents in Tampines North.

Similar action was taken in 1999, when then-Jalan Besar GRC MP Choo Wee Khiang resigned his seat in Parliament before he was convicted of a cheating offence.

The three remaining MPs in Jalan Besar GRC - Dr Lee Boon Yang, Dr Yaacob Ibrahim and Mr Peh Chin Hua - took over Mr Choo's duties in the Whampoa division.

GOH CHIN LIAN