Activist and comedian Eddie Izzard called for Labour to "stamp out” the “stain of anti-Semitism" as the party distanced itself on Sunday from anti-Semitic, pro-Jeremy Corbyn Facebook groups.
"This is a very important time for the Labour Party and we must stamp out completely the stain of anti-Semitism from a minority of members. It has no place in our party," Mr Izzard said.
Mr Izzard was appointed to Labour's national executive committee following the resignation of Christine Shawcroft, an ally of Labour leader Jeremy Corbyn who stepped down on Saturday following an anti-Semitism row.
“We must unite our party around the platform of hope that Jeremy Corbyn has built so that we can kick out this terrible Tory government and build a Britain for the many, not the few,” Mr Izzard said.
His comments came as The Sunday Times reported that a dozen officials working for Labour belonged to Facebook groups that have posted messages considered anti-Jewish, violent or abusive, including praise for Adolf Hitler.
The report followed a two-month investigation into the 20 largest pro-Corbyn Facebook groups. A Labour spokesman said the groups were not connected to the party in any way. There was no suggestion that the Labour members supported or posted the offensive Facebook messages.
Separately, Labour donor Sir David Garrard told The Observer that he left the Labour party over its failure to confront "the most blatant acts of anti-Semitism".
Mr Garrard, who has donated £1.5 million (7.7m dirham) to Labour since 2003, reportedly said: "I have watched with dismay and foreboding the manner in which the leadership has, in my view, over the last two years, conducted itself."
Mr Corbyn, a critic of Israeli actions against the Palestinians, maintains that Labour has "zero tolerance" for anti-Semitism.
The accusations have escalated since last week, however, when a six-year-old Facebook post came to light. In 2012, Mr Corbyn posted a Facebook message backing the creator of a mural that included a number of anti-Jewish stereotypes.
Mr Corbyn later said that he regretted not looking closely at the "deeply disturbing and anti-Semitic" mural before encouraging the artist.