Steven Woolfe, a leading candidate to become the new leader of Britain's UK Independence Party, collapsed and was taken to hospital in Strasbourg after an "altercation" during a heated meeting about the party's future.
Woolfe, was involved in the altercation at a meeting of UKIP members of the European Parliament (MEP) to discuss the direction of the party, riven by factional infighting since Britain voted to leave the European Union in June.
He collapsed and lost consciousness outside the EU legislature chamber after leaving a voting session, a parliamentary official said. He was treated at the scene by the legislature's first responders and taken to a local hospital.
Neil Hamilton, the party's Welsh leader told BBC TV, that he understood Woolfe had suffered bleeding on the brain.
A UKIP spokesman said his condition was improving. "It looks like he's getting better," the spokesman said.
Pictures from ITV showed Woolfe sprawled face down, still clutching a briefcase on a walkway in the parliament building containing MEPs' offices.
"I deeply regret that following an altercation that took place at a meeting of UKIP MEPs this morning that Steven Woolfe subsequently collapsed and was taken to hospital. His condition is serious," party leader Nigel Farage said in a statement.
Steven I think picked a fight with one of them and came off worse
Jonathan Arnott, a UKIP MEP, told London's LBC radio the party had held a meeting to discuss "where we were going to go" and Roger Helmer, another at the meeting, said there had been "a lively exchange of views".
'Hit head on window'
Hamilton, who was not at the meeting but said he had been given an account of what had happened by an eyewitness, had been knocked over and hit his head on a window.
"Steven I think picked a fight with one of them and came off worse," Hamilton told BBC TV. "It's most unfortunate but passions obviously run high."
UKIP has 22 MEPs, two more than either the ruling Conservatives or opposition Labour, after winning the May 2014 European Parliament election on a surge of eurosceptic sentiment that saw former prime minister David Cameron agree to hold a referendum on quitting the EU.
Farage, who leads UKIP in the European parliament, resumed his overall leadership of the party on Wednesday when his elected successor stood down after 18 days in the job amid factional struggles following June's referendum which delivered UKIP's key goal of taking Britain out of the European Union.
Woolfe, who was celebrating his 49th birthday, had said he would be putting his name forward to be the party's new leader but admitted he had been considering joining Prime Minister Theresa May's ruling Conservatives.
"I have been enthused by the start to Theresa May's premiership," he said in a statement announcing his candidacy.
"In the last few weeks I have thought long and hard about my political future and how I can best help build the Brexit Britain we voted for in June - a meritocratic, independent and prosperous country that stands up for the millions of people who have been ignored for too long."
Woolfe had been the original favourite to take over from the charismatic and well-known Farage who announced he would step down after the vote for Brexit, but was excluded from the leadership ballot after submitting his nomination papers late.
In his absence, Diane James was elected leader but quit after less than three weeks saying she did not have sufficient authority or the full support of UKIP MEPs.
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