The Democratic Alliance (DA) announced on Tuesday that veteran politician Patricia de Lille has ceased to be a member of the party and lost her job as mayor of Cape Town, in a decision that she promptly vowed to challenge in court. 

She told a media briefing: "I am ready to fight", even as deputy mayor Ian Neilson was shifting into the position she has held for seven years. 

The DA said Neilson would serve as acting mayor but it would move with speed to elect a permanent mayor to provide stability to a local government shaken by months of open warfare between De Lille and the party.

She is expected to launch a court challenge on Friday against the party's decision to oust her on the basis of remarks made in a radio interview late last month.

Natasha Mazzone, the deputy chairperson of the DA's federal council, earlier told a media briefing the "cessation of her membership" was the result of the mayor breaching section 3.5.1.2 of the party's constitution. It stipulates that a member ceases to be a member when he or she "publicly declares his or her intention to resign and/or publicly declares his or her resignation from the Party” and therefore De Lille's assertion that she was "ready to walk away" sealed her fate, Mazzone said.

Mazzone quoted from an interview with 702 Radio on April 26 where De Lille told Eusebius McKaiser that she would resign from the country's second biggest party as soon as she had cleared her name in a bitter dispute with its leadership.

"I’ve said it many times before, Eusebius, you know, the writing’s on the wall that people don’t want me for whatever reason... I will walk away," De Lille was recorded as saying in the interview.

James Selfe, the chairman of the DA's federal executive, conceded that he did not think the decision to terminate De Lille's membership of the party would be the end a bruising battle between her and the DA, which has repeatedly landed up in the Cape Town High Court.

"I would like to think that the saga ends today, but somehow I doubt it."

The clash between De Lille and the DA leadership began last year when colleagues at the city council aired maladministration and corruption allegations against her. Two of her allies in the city administration lost their jobs following an internal investigation but De Lille has strenuously denied any wrongdoing. 

She has accused the party of trying to oust her to frustrate efforts to bring about greater social equality in the city, earning a stinging rebuke from Selfe who told media the claim was nonsense.

But on Tuesday after the party ousted her, she reiterated the accusation.

De Lille said the decision to kick her out was a victory for conservatives within the DA.

"If they think it's a victory today, it's a victory for the conservative people in the DA who don't want to see transformation in the City of Cape Town."

De Lille has in recent weeks sought to force the DA through the courts to give her access to documentation that informed its decision, on February 14, to charge her with misconduct after a separate political investigation, headed by DA chief whip John Steenhuisen.

Mazzone said on Tuesday it had hoped the disciplinary process would be concluded within two months but that De Lille had chosen to challenge the process repeatedly by "introducing a number of interlocutory matters, including that the hearing be open to the public and that it should be conducted by independent persons".