Tommy Sheridan has cut his ties with the Scottish Socialist Party and launched a new rival organisation.
Tommy Sheridan helped launch his new party at the weekend
Solidarity was unveiled at the same Glasgow hotel where an SSP rally on Saturday told members there was no justification for the split.
The new party will be led by SSP co-founder Sheridan along with fellow Socialist MSP Rosemary Byrne.
They hope it will initially attract as many as 700 SSP members and many leading trade unionists.
The split comes in the wake of Mr Sheridan's court victory against the News of the World which claimed he visited swingers clubs and cheated on his wife Gail.
The case saw several SSP members, including MSPs, tell the jury that he admitted to attending a swingers club at a party meeting.
This prompted Mr Sheridan to accuse them of helping engineer "the mother of all stitch-ups".
At Saturday's SSP rally, the party's convenor Colin Fox said the new party had been created by Mr Sheridan because he did not stand a chance of winning back the role as SSP leader.
Mr Fox said: "The SSP as a party achieved a historically remarkable project, we brought the left together, something the left on a British-wide basis was unable to achieve.
"The paradox is that now it is best for Tommy Sheridan and the SSP to separate because of the damage that being associated with Tommy Sheridan would do to the SSP.
"Neither I nor the vast majority of SSP members have been persuaded of the case Tommy Sheridan puts forward for another party with an identical political programme."
Mr Sheridan told BBC Scotland: "If I and others had stayed and fought within the SSP, then by the time of the October conference, we would have inherited a carcass.
"Because the blood-letting is so deep and so serious that it really is an animal that has run out of steam. It has run out of breath."