Labour has to move fast to replace Ron Davies

In theory, the party's Welsh executive could impose a candidate, but that is highly unlikely.

A party spokesman said it was more probable that the recent selection procedures in Ogmore and Swansea East - after the deaths of MP Sir Ray Powell and AM Val Feld respectively - would be followed.

That would mean the Welsh executive inviting applications from interested party members. A discussion would then follow between Wales Labour officials and senior officers in the Caerphilly party to draw up a shortlist.

Tight timetable

The shortlist would then be presented to the 600 party members in Caerphilly. They would then choose their candidate through a one-member-one-vote ballot.

The Caerphilly party will hold an extraordinary general committee meeting this Friday evening. It will also be attended by Wales Labour Party officials, and the two sides will discuss the selection process.

The process must be completed very quickly because of the impending Assembly election. All nominations for the election must be registered by 1 April.

(Standing for the Assembly) is something that I will consider Jeff Cuthbert, local party chairman

This tight timetable suggests that the new Labour candidate could be known within a week.

Much speculation centres on the likely candidates.

But one name linked with the vacancy who has ruled herself out is Delyth Evans, the Mid and West Wales AM who replaced former First Secretary Alun Michael after he stepped down three years ago.

Ms Evans announced a year ago that she would leave the Assembly at this election to spend more time with her family.

She said she had come under a lot of pressure to stand and had considered doing so, but she was sticking to her original intention.

Jeff Cuthbert, the local party chairman, has not yet decided whether to stand. He told BBC Wales News Online: "I can't say at this stage. It's all happened very quickly.

"It's something that I will consider but I can't make a decision at this stage."

Mr Cuthbert, who is a senior official at the Welsh exam board the WJEC, said he would decide shortly whether to put his name forward.