UKIP leadership hopeful Steven Woolfe in Strasbourg hospital

The 49-year-old MEP said in a statement that a CT scan had shown that there was no blood clot on his brain but that he was being kept in hospital overnight as a precaution.

"At the moment I am feeling brighter, happier, and smiling as ever. As a precaution, I am being kept in overnight awaiting secondary tests to make sure everything in fine," he said.

"I would like everyone to know that the parliamentary staff, the Ukip MEPs with me and hospital staff have been brilliant. Their care has been exceptional.

"I am sitting up, and said to be looking well. The only consequence at the moment is a bit of numbness on the left hand side of my face. "

It is understood that Mr Woolfe passed out after suffering what were described as two "epileptic-like fits" as well numbness on the left hand side of his body.

In his statement he made no reference to the reported altercation which took place at the European Parliament in Strasbourg.

There were unconfirmed reports that he was punched during the course of an argument while other reports suggested he hit his head after falling heavily.

A spokeswoman for French national police said that the incident had not been reported to them and they had no current plans to investigate.

"If someone decides to ring and make a complaint, we will of course follow it up," she said.

A spokeswoman for the European Parliament confirmed Mr Woolfe had collapsed in the main building in Strasbourg, and said that an investigation into the circumstances was now under way.

The incident nevertheless left MEPs and activists reeling in a party which has at times appeared to lurch from one crisis to another.

Earlier, party leader Nigel Farage disclosed that Mr Woolfe's collapse followed a confrontation at a meeting of Ukip MEPs.

"I deeply regret that, following an altercation that took place at a meeting of Ukip MEPs this morning, Steven Woolfe subsequently collapsed and was taken to hospital. His condition is serious," he said.

MEP Roger Helmer, who was at the meeting, confirmed there had been "a lively exchange of views" but said he did not see any physical confrontation.

He said the incident took place "a good two hours" before Mr Woolfe collapsed during a voting session at the parliament.

"There were some lively exchanges of views. I think you'll find that's not uncommon in political meetings. I certainly saw no physical altercation take place," he told the BBC.

"We had a typical, general discussion about the previous leadership elections, the situation following Diane James stepping down, and obviously the steps we need to take to get a new leader in place."

Neil Hamilton, the Ukip leader in the Welsh Assembly, who was not present, said he had been told Mr Woolfe "toppled over and hit his head on a glass window" after the confrontation.

"It must have been quite a wallop, I guess, to have had the impact that it seems to have had," he told the BBC.

The incident is a further body blow for a party that was already in the grip of a leadership crisis following the shock resignation of Ms James just 18 days after she was elected to the post.

Mr Woolfe, the party's immigration spokesman, was the first contender to throw his hat in the ring having been barred from standing in the last leadership election after it was ruled he submitted his nomination papers 17 minutes late.

There were claims that he had angered some MEPs by admitting that he had considered defecting to the Conservatives before declaring his candidacy.

In a statement, Mr Woolfe said he had been "enthused" by Theresa May's start to her premiership, which had prompted him "as it did many of my friends and colleagues, to wonder whether our future was within her new Conservative Party".

The incident comes against a background of bitter rivalry and feuding within the Ukip ranks - with many senior figures openly at odds with each other.

Feelings were already running high, with some in the party deeply unhappy at Mr Farage's decision to carry on as interim leader until a permanent successor was in place.

The only other candidate to declare so far, Raheem Kassam - a former aide to Mr Farage - warned that the party could not look forward to a positive future unless it was able to heal the "internal fractures".

"There are so many people shaking hands with one another and then knifing them in private. It has to stop," he said.

"I'm clear about what I stand for: a strong, united Ukip, free of the Tory splitters ... I'm sick of the backstabbing and negative briefings. If I have something negative to say about someone, I'll say it to their face, not behind their backs."

Mr Hamilton, who has long been at odds with Mr Farage, described the abuse within the party as a "cancer" which needed to be stamped out.

"There is, actually, too much violence going on in Ukip generally at the moment. I don't mean physical violence, but stuff which is being traded online, some pretty unpleasant things that are being said," he said.

"This is a cancer which must be stamped out in the party - should have been stamped out already."

• Steven Woolfe has emerged from his place in the pack as Ukip's immigration spokesman to become a favourite for the leadership.

The 48-year-old barrister, who is of mixed race and was born and brought up in the North, is regarded by many within Ukip as a candidate able to broaden the party's appeal beyond its southern and middle-class core.

He has been the party's MEP for North West England since July 2014.

As the Ukip candidate for Labour-held Stockport in 2015, Mr Woolfe finished third with 13.1% of the vote.

Before the election, there were signs he could be a front-runner to succeed Nigel Farage when the party put his name forward to stand in in a lived televised debate after the leader pulled out for "family reasons", though Channel 4 denied the request.

And he was tipped to win the recent leadership contest before he was barred for submitting his nomination papers 17 minutes late, which he blamed on technical difficulties.

The decision by the party's National Executive Committee brought its rival factions out into the open and Mr Woolfe, who said he was "extremely disappointed" by the move, branded the NEC "not fit for purpose".

His supporters claimed Mr Woolfe had been the victim of a coup led by Ukip's only MP, Douglas Carswell, and Neil Hamilton, group leader in the Welsh Assembly.

He was the first leadership contender to throw his hat in the ring following the shock resignation of Diane James this week.

According to his personal website, he was born on October 9, 1967, in Moss Side in Manchester, and grew up in Burnage as the eldest of a family of four.

He went to school at St Bede's RC Independent College and later studied law at Aberystwyth University before beginning his legal career at chambers in Inner Temple.

Before politics, Mr Woolfe worked as a lawyer in the City of London and acted as counsel for hedge fund managers, as well as a consultant to financial institutions.

He was embroiled in controversy earlier this year after it emerged he had admitted failing to declare a drink-driving conviction when he stood for a police and crime commissioner post.

Mr Woolfe said he "forgot about the conviction" when he stood in the Greater Manchester PCC election in 2012, in a possible breach of electoral law, but police said he would not face any action.