Strasbourg, France: A top candidate to lead Britain’s anti-EU UK Independence Party (Ukip), Steven Woolfe, collapsed and was taken to hospital Thursday after an “altercation” at the European Parliament, former chief Nigel Farage said.

The incident came just a day after Ukip’s new leader Diane James quit unexpectedly only 18 days into her reign as Farage’s successor, as the party grapples with infighting following Britain’s vote to leave the European Union.

Farage said Woolfe was in a “serious” condition in hospital “following an altercation that took place at a meeting of Ukip MEPs this morning” at the parliament.” He did not give further details.

A Ukip spokesman said Woolfe “was taken suddenly ill in the European Parliament building in Strasbourg this morning. He has been taken to hospital in the city and he is undergoing tests.”

European Parliament spokesman Jaume Duch told journalism that Woolfe “fell ill in a corridor at the parliament near the hemicycle (main chamber). He was taken to hospital.”

Asked whether there had been a fight he said “we do not have that information”.

The party has faced an existential crisis since pushing Britain towards a referendum on June 23 in which the country voted to quit the EU, and since Farage’s resignation shortly afterwards.

James only became leader after Woolfe, her main rival, was dramatically ruled out of the contest after failing to submit his application in time.

Woolfe, who had been supported by both Farage and Arron Banks, the party’s main financial backer, was quick to throw his hat into the ring to replace James on Wednesday.

“Only a strong Ukip can guarantee Brexit is delivered in full,” Woolfe said in a statement.