KARIE Murphy, the frontrunner to be Labour's General Election candidate in Falkirk, the seat held by disgraced MP Eric Joyce, has dramatically pulled out of the race for the candidacy.

The development marks another twist in a troubled campaign been dogged by controversy surrounding Labour's candidate.

A senior party source said: "Karie Murphy is now not going to run." He was unable to provide a reason.

The source acknowledged Ms Murphy, a former Unison official who runs the office of high-profile Labour MP Tom Watson, was the favourite to fight for what has been a safe Labour seat, but stressed an announcement on the candidacy would be made soon.

"We will make an announcement in the near future. Wait and see," he added.

Ms Murphy's withdrawal leaves two other contenders in the race: Linda Gow, a former Falkirk Council leader, and Gregor Poynton, UK political director for communications firm Blue State Digital.

Ms Murphy, who had been heavily backed by the Unite trade union, hit the headlines when she said she would throw a party to mark the passing of Baroness Thatcher.

A photo of the late Conservative Prime Minister, who passed away last month, was posted on the left-winger's Facebook page in January and carried the words: "One Hellbound Bitch!"

Next to the picture, Ms Murphy wrote: "Having a party when she dies ..."

After The Herald made inquiries about the entry, the Facebook account was deactivated.

The Scottish Conservatives branded the posting disgraceful and urged Labour to distance itself from it.

The process of finding a candidate in Falkirk has been plagued by controversy. Eric Wilson, a senior UK party official, was drafted in to sort out what has been dubbed a "gigantic mess" in Labour's selection process.

The party called time on a local consultation into whether an all-women shortlist should be used for the safe seat, after complaints the survey was flawed.

Unite paid for the survey –a decision some members believed was a "stitch-up" by the union to ensure Ms Murphy obtained the candidacy.

One Labour source said: "To call this selection process a gigantic mess would be an understatement."

In a separate development, the Scottish party leadership intervened over the large number of new members who had joined the Falkirk party.

One report suggested Unite had recruited "well over 100 members" to the constituency party last year.

In a letter to new members, Mr Wilson said: "There have been concerns raised about the con-siderable number of new members who have joined the local party since July 2012. There have also been questions raised about the validity of some of these new applications."

Last month, Richard Bryce, the local party vice-chairman, resigned his post citing divisions within the branch.

The vacancy for a new Labour candidate arose after Mr Joyce, 52, left the party last year after being fined £3000 for assaulting a Tory MP in a Commons bar in February 2012.

In March, the Independent backbencher spent a night in police cells after a second incident in a Commons bar during which he wrestled with two police officers.