It was Mr Reynolds' promotion of Mr Whelehan last Friday that caused the Labour Party to quit the coalition government.
Bertie Ahern, the Fianna Fail Finance Minister, is favourite to take over from Mr Reynolds, who is likely to remain as leader until a party meeting on Saturday to choose a successor. Mr Ahern is expected to face a challenge from Maire Geoghegan-Quinn, the Justice Minister.
John Major wrote to Mr Reynolds yesterday praising his role in the Northern Ireland peace process and emphasising Britain's determination to press ahead with the initiative. However, there was concern among senior British ministers at the possibility that Dick Spring, the Labour leader and Irish Foreign Minister, may not serve in any new Irish government.
In his letter to Mr Reynolds, Mr Major wrote: ``I know that others will carry on where you have left off; and I know that you will continue your committed support for the process.''
But many uncertainties remain before a new government can take shape. Last night brought another bizarre twist when news of Mr Whelehan's resignation caused speculation that Mr Reynolds might yet be resurrected from the political dead. This seemed most unlikely, as Labour Party sources indicated they were not prepared to serve under him.
Yesterday morning Mr Reynolds bade a poignant farewell to power in the Dail, saying he looked forward to spending more time with his family. He announced his intention to resign as it became clear that substantial sections of his party were in favour of his departure.
On Wednesday night he admitted to the Dail that he had given an inaccurate account of the failure to extradite a Catholic priest, Fr Brendan Smyth, to face child sex-abuse charges.
There is as yet no sign of a general election as complicated manoeuvres began to elect a new Fianna Fail leader. This is expected to be a prelude to a period of horse-trading aimed at stitching together a new coalition.
In Dublin last night the most likely outcome appeared to be the election of Mr Ahern as successor to Mr Reynolds, followed by a new Ahern-Spring coalition. One looming deadline falls on Tuesday, when the Dail resumes. One possible problem is that Labour might find Mr Ahern unacceptable because he was also aware that the Dail had been misled about the Smyth case.
Other possibilities included a ``rainbow coalition'' of smaller parties excluding Fianna Fail or, if all negotiations fail, a general election.
Mr Spring, who remains pivotal to any new arrangement, said: ``The options are that you put some form of government together, or you fail to put a government together and then you have an election. It's all very simple - sitting down to do it isn't that simple, mind you.'' In radio and television interviews yesterday he steadfastly declined to comment on which Fianna Fail candidates might be acceptable to him. ``I'm not in the position of qualifying or disqualifying people from co-operating with the Labour Party,'' he said.
The weekend is expected to be a period of both stocktaking and political manoeuvring after an extraordinary week in Irish politics. One Fianna Fail backbencher, Micheal Martin, said: ``There's a sense of bewilderment and a sense of disbelief, still, that this has happened. It's still baffling me.''
The general feeling last night was that the peace process was unlikely to be threatened in the medium term.