Nigel Farage has said he will not stand to replace Paul Nuttall as Ukip leader.
The three-time leader acknowledged his habit of resigning and returning to the role had become an "ongoing joke", adding: "To return now would be premature."
He said the threat of violence and the "amateur shambles" of the party's ruling national executive committee were the main factors in his decision not to stand.
Mr Nuttall resigned following a disastrous general election in which the party won just 1.8% of the UK vote share and no Commons seats.
Writing in the Sunday Telegraph, Mr Farage left the door open to an eventual return if a "full and proper" Brexit was not delivered.
"It is already something of an ongoing joke about the number of times I have stood for the leadership and resigned," he said.
"To return now would be premature. But I'm still committed to the great Brexit battle and I will continue in my role as the leader of a group in the European Parliament, overseeing the Brexit process.
"In many ways, what happens in that parliament over the next two years is perhaps as important as everything that goes on in Westminster.
"Of course I want a full and proper Brexit, and if in 2019 we reach the end of the Article 50 process and a huge gap is left, whether that is not taking back our fishing rights, the continuation of free movement or still paying Brussels too much money, I would not hesitate in throwing myself back into the front line of domestic politics."
Mr Farage urged Ukip to reform its internal structures or face dying.
"If it does not sort itself out and make the changes necessary to become a professional, modern political party, and if then we find ourselves with a Brexit that falls short of the mark, another vehicle will then come along to replace it," he said.