Jeremy Corbyn’s most senior aide joined a Facebook group littered with antisemitic references to Israel – including a comparison between Gaza and the Nazi death camp Belsen.

Karie Murphy – who is the Labour leader’s chief of staff – remains a member of the group, called “Johnny Rotten you ain’t no human being if u play the Israeli fascist regime” and set up in 2010 to campaign to stop the former Sex Pistols singer from playing a concert in the Jewish state.

Records unearthed by investigator Iggy Ostanin show that Ms Murphy joined the group at the time it was first set up and has failed to quit despite the appearance of extreme antisemitism in comment threads.

One post by an individual named Ian Weniger states: “ Gaza is the new Belsen... get with the program, John/Johnny.”

Another, by Laila Patricia Kent, reproduces the name of the Facebook group, a crass rewrite of the Sex Pistols song God Save The Queen: “Johnny Rotten you ain't no human being if you play for the Israeli fascist regime…”

A group member named Yael Kahn writes: “More from the mouth of this boycott breacher and his words are music to apologists for the Israeli crimes. He is in denial of how his crossing the Palestinian picket line of their call for cultural boycott is indeed serving the Israeli state. But this isn't surprising given the racist excuses he had given for his actual support to the Israeli regime in another interview.”

Another member of the group David Rockerchild states: “ You're a f***ing c**t if you play Israel, Johnny!”

Ms Murphy, a key ally of Unite the union leader Len McCluskey, first rose to prominence in 2013 when she tried to become Scottish Labour's candidate in Falkirk after then MP Eric Joyce was expelled.

Alongside Seamus Milne, Labour’s director of communications, Ms Murphy is now said to be Mr Corbyn’s most trusted aide.

Labour sources say Ms Murphy has previously claimed some complaints of antisemitism are being used as a vehicle to attack Mr Corbyn. 

She was one of those to argue against the decision to drop disciplinary action Jewish MPs such as Dame Margaret Hodge after she labelled the Labour leader an “antisemite”.

Last week it was announced she would be filling in for general secretary Jennie Formby, who is stepping back from her role during her treatment for cancer.

The campaign to stop Johnny Rotten, whose real name is John Lydon, from playing Israel emerged after the singer conducted an interview in which he said: “If Elvis-f***ing-Costello wants to pull out of a gig in Israel because he’s suddenly got this compassion for Palestinians, then good on him. But I have absolutely one rule, right? Until I see an Arab country, a Muslim country, with a democracy, I won’t understand how anyone can have a problem with how they’re treated.”

In August 2010 he played a concert in Tel Aviv with his band Public Image Ltd.

Labour sources said on Monday that Ms Murphy had now left the Facebook group after being alerted to her membership of it – which they said she had not been aware of.