Before Monday night, Mr Davies was just about guaranteed to become the first "prime minister" of Wales. Earlier this year the Welsh Labour Party chose him as its leader and candidate for the post of first secretary of the new Welsh Assembly, which is due to be elected next year.

The political consensus is now rapidly converging around the view that if Mr Davies' error of judgement was severe enough for an immediate cabinet exit, it is untenable for him to stay as Labour's leader in Wales.

So Tony Blair faces a new headache. The Welsh Labour Party, like Labour in Scotland, has a habit of causing the occasional problem for Tony Blair.

It sees New Labour as an English creation. But Labour's problem now is that any new leader of the Welsh party must come from its list of prospective assembly candidates.

The selection process to get on that list is over and done with. Finding someone prominent and popular enough on it who Mr Blair would also feel comfortable having in a leadership position will prove difficult.

New Welsh Secretary Alun Michael is not standing for election to the Assembly - and has made it clear he does not want to change his mind.

Ron Davies, a left-winger, would by no means have been Mr Blair's first choice to lead the party in Wales - but the alternative, from the Labour leader's point of view, was worse.

Rhodri Morgan, the popular backbencher who put up a strong challenge to Mr Davies in the contest to lead the party in the assembly, is now in with a second chance.

The Cardiff West MP is noted for his effective chairmanship of the Public Administration Committee and independence of mind - which is why by Wednesday morning the Labour leadership had mounted an "Anyone but Rhodri" operation to seek an acceptable figure to back.

Wayne David: Proved his loyalty in the past

Wayne David, currently serving as an Euro-MP but accepted as a prospective assembly candidate, is one assembly name the leadership could throw its weight behind.

Mr David has previously proved his loyalty as leader of the European Parliamentary Labour Group.

But he was not seen as a great success in the role, and does not have Mr Morgan's profile or popularity in Wales.

And, that is about it.