Ukip's Steven Woolfe has announced he is quitting the party, deeming it "ungovernable".
Woolfe said the party "lacks direction, it lacks a purpose and it lacks any semblance of professional organisation". He said he will now sit as an independent MEP in the European Parliament.
Earlier today, party chairman Paul Oakden said Ukip may still be without a leader by Christmas, as it battled to overcome the recent turmoil.
Steven Woolfe had been the favourite to take over from leader Nigel Farage, but was hospitalised in Strasbourg following an "altercation" with another of the party's politicians, Mike Hookem. Woolfe said he was seeking legal advice over the incident.
"What happened in Strasbourg, combined with the infighting and toxicity since the summer, have demonstrated to me one cold, hard fact. Ukip without Nigel Farage leading it and the Brexit cause to unify has resorted to damaging infighting."
"Indeed, the party I joined in 2011 is now ungovernable. The last few weeks and months have demonstrated that it lacks direction, it lacks a purpose and it lacks any semblance of professional organisation."
Woolfe had believed he was the person to "give Ukip a new lease of life in the post-Farage, post-referendum era", but felt disillusioned now as the party was in trouble and he did not want to be the one to lead it.
Farage's successor Diane James stepped down earlier this month, after just 18 days in the role. She said it had "become clear that I do not have the sufficient authority, nor the full support of all my MEP colleagues and part officers" to pursue changes to the party.
Ukip leadership candidate and former senior adviser to Farage, Raheem Kassam said Woolfe had "been under a lot of pressure from people negatively campaigning against him inside the party". He said: "I sympathise with his feeling that he has been effectively pushed out" and that those who were at fault "should hang their heads in shame".
He also said that some form of internal disciplinary process should have occurred following the altercation at the European Parliament.