The former Workers' Party secretary-general was rushed to the Tan Tock Seng Hospital at about 1.30am after he had complained of breathing difficulties, but doctors were unable to revive him.

Mr Jeyaretnam leaves behind two sons, Kenneth, a banker, and Philip, a lawyer. His wife Margaret Cynthia Walker, also a lawyer, died from cancer in 1980.

His niece, who gave her name only as Kavinia, said he had not been feeling well for the past three weeks.

But on Monday, he was at the High Court attending to two cases there, said the opposition stalwart's longtime friend, Mr Ng Teck Siong who was with him.

Said Mr Ng: 'I was with him in court the whole day, but he wasn't feeling well and he adjourned his case at around 4pm.'

Mr Jeyaretnam's death not only came as a shock to many in the political scene but has also left questions over his newly formed Reform Party and his efforts to push for a by-election in Jurong GRC following the death of one of its MPs, Dr Ong Chit Chung from the ruling People's action Party on July 14.

He was supposed to appear in the High Court on Oct 15 to argue for a by-election to be held in the constituency, on behalf of a WP supporter and Jurong GRC resident.

Earlier in July, Mr Jeyaretnam had also challenged the Government to defend the Singapore system against its critics by calling a by-election.

The issue was debated in the Parliament last month, after law professor and Nominated MP Thio Li-ann filed a motion calling for the law to be amended to require that a by-election be called when the minority MP is no longer on the GRC team, or when at least half the MPs in a GRC vacate their seats mid-term.

The motion was defeated after a debate.

Mr Ng, who is the Reform Party's organising secretary, said the party's central executive committee will meet next week to decide on the High Court application and also on who to fill Mr Jeyaretnam's post.

He broke the PAP's 15-year monopoly of the Parliament in 1981 when be became MP for the now-defunct Anson ward.

Of the five General Elections since then, he has contested only once, in 1997.

He finished as top loser through the bruising Cheng San GRC bout, earning a 45.2 per cent of the valid votes.

That brought him back into the House as a Non-Constituency MP, a brief tenure that ended in 2001, when he was declared a bankrupt for failing to pay about $600,000 in damages from defamation suits against him by PAP politicians.

Since then he had been barred from contesting in elections.

He discharged himself from bankruptcy last year, and set up the Reform Party in April this year as his political comeback vehicle.

Mr Desmond Lim, acting secretary-general for Singapore Democratic Alliance and assistant secretary-general of Singapore People's Party, sent condolences to Mr Jeyaretnam's family on Tuesday.

Said Mr Lim: 'Sorrow fills our hearts at this sad moment, a sorrow that is deep and personal. The news of the untimely death of Mr Jeyaretnam comes as a great shock. His departure was sudden, unexpected and particularly distressing.

'All of us in the fraternity have suffered a great loss.'

Mr Sebastian Teo, president of the opposition National Solidarity Party, described Mr Jeyaretnam as a respectable opposition figure who wanted to contribute to the country despite his age and several setbacks.