Nathan Gill leaves UKIP assembly group to sit as independent
UKIP Wales leader Nathan Gill has announced he is leaving the party's group in the Welsh Assembly to sit as an independent AM for North Wales.
But he said he was not leaving the party and would remain a UKIP MEP.
Mr Gill said he was leaving the UKIP Senedd group as "infighting" had become a "distraction" from its work.
UKIP group leader Neil Hamilton said he did not think Mr Gill's decision would make "much difference", claiming: "We don't see him much in the assembly."
Meanwhile, Lisa Duffy, one of the candidates considered to be a front runner in UKIP's leadership election, called for Mr Gill to resign from the party.
A rift emerged between the two men when Mr Hamilton was chosen by a majority of UKIP's seven AMs to lead them in the Senedd following the election in May.
Five of the group called on Mr Gill to honour his pledge to give up his seat in the European Parliament if elected to the assembly.
However, Mr Gill has insisted he can carry out both roles.
The North Wales AM had been threatened with expulsion from UKIP if he did not give up one of his two elected posts, with party bosses arranging for a vote of members in Wales to decide his future.
"After much deliberation I have decided to break away from the UKIP group in the Welsh Assembly and sit as an independent," Mr Gill said in a statement on Wednesday.
"Too much time has been wasted on infighting over issues that cannot be resolved and it has become a distraction to the work we were elected to do.
"I remain UKIP leader in Wales and am committed to serving my constituents."
Responding to the news, Mr Hamilton said: "I haven't been officially informed - his letter must have got lost in the post.
"We'll have to do our best to survive without him - we don't see him much in the assembly so I don't think we'll notice much difference."
UKIP Wales chairman Chris Smart called Mr Gill's departure from the party's assembly group "inevitable".
"Nathan has played no part in the group and did not attend yesterday's group [meeting]," he said.
"He should now resign from the assembly having been elected as a UKIP member."
Assembly rules do not require AMs leaving a political group to resign and seek re-election.
In 2009, Plaid Cymru AM Mohammad Asghar defected to the Conservatives, while a number of AMs have sat as independents - some temporarily - after disputes resulting in suspension from their party groups.
Despite Mr Gill saying he is still UKIP Wales leader, a member of the the party's National Executive Committee (NEC) said that is not the case, with the post becoming vacant when Mr Gill was temporarily expelled.
"The office of leader in Wales thus currently remains vacant," said Tomaz Slivnik.
Leadership candidate Ms Duffy said Mr Gill does not have "much option" other than to resign from the party.
Ms Duffy, a town and district councillor in Cambridgeshire, said: "From the party's point of view, if he was a councillor he would have been asked to leave the party today."
Speaking ahead of a campaign hustings in Newport on Wednesday, she said the UKIP NEC made the right decision in balloting on whether it was acceptable for Mr Gill to hold an AM and MEP job.
"Because they have been put there and elected as UKIP - if he had been elected as Nathan Gill, no - but he has been elected under the UKIP brand," she added.
"So for me, you do the honourable thing and you resign and you allow the residents, the voters, to make the decision as to who they want," she said.
Analysis by Paul Martin, BBC Wales political reporter
This is a culmination of months of arguments between Nathan Gill, the face of UKIP's assembly election campaign, and Neil Hamilton, who beat Mr Gill in a vote to become the party's assembly group leader.
There have been public disputes on several matters since then - Mr Gill's camp attacking Mr Hamilton for not living in Wales, while Mr Hamilton and his supporters criticise Mr Gill for serving as both an AM and an MEP.
The two factions also represent a wider split in UKIP - in simplistic terms, wings of the party which are for and against outgoing leader Nigel Farage.
I am told Mr Gill mulled this over while away on holiday last week and has decided enough is enough.
The tone of Mr Hamilton's response illustrates how sour the relationship has become.
So, just over three months since the assembly election, the UKIP group is down from seven to six - the breakdown all about personality rather than policy.