Jeremy Corbyn’s period at the head of Labour has been punctuated by a series of rows about antisemitic episodes, a toxic subject that has continued to trouble the party leadership despite an internal inquiry, numerous suspensions and repeated apologies.

The disputes are often fuelled via social media, or by trawling through postings from years ago – and made especially potent because the subject is frequently seen through an internal left-right prism, of loyalty or otherwise to the man who has led the party since 2015.

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Against that backdrop, Corbyn’s Sunday night statement that the discriminatory sentiment has existed “in pockets within the Labour party” is significant, even though it was made after it emerged that he had appeared to condone an antisemitic mural in a Facebook posting from 2012.

It was not meant to be like this. A debilitating period of antisemitic rows had prompted Corbyn to ask Shami Chakrabarti to conduct a party inquiry in the spring of 2016 in an attempt to draw a line under the issue at a time when over a dozen members had been suspended.

One of those was Naz Shah, the MP for Bradford, who had suggested relocating Israel to the US in a Facebook posting made in 2014 before her election to parliament. Soon afterwards, Ken Livingstone waded in, repeatedly and stubbornly arguing that “Hitler supported Zionism” at the time the Nazi leader rose to power.

Shah subsequently apologised for her postings and her suspension was lifted – but Livingstone, who was once a Corbyn ally, remains suspended. The former London mayor is one of many members who have spent more than a year awaiting an expulsion hearing, many of whom come from the party’s left and have historic links with Corbyn or the pro-Palestinian movement long supported by the party leader. His suspension, which had been due to end in April, was extended this month after Labour announced a fresh investigation over separate complaints.

Corbyn’s critics view the Chakrabarti inquiry as a missed opportunity. When it concluded, Corbyn spoke in terms that failed to persuade those concerned about antisemitism that he was sufficiently conciliatory, and made an unnecessary semi-equivalence. “Our Jewish friends are no more responsible for the actions of Israel or the Netanyahu government than our Muslim friends are for those of various self-styled Islamic states or organisations,” he said in a pre-prepared speech.

Corbyn’s team later clarified that in his remarks he had been referring to states of an Islamic character, such as Saudi Arabia, Iran or Hamas in Gaza. But the Board of Deputies said it heard something different, voicing unhappiness that the party leader had established “some sort of equivalence” between Israel and Islamic State.

In her report, Chakrabarti concluded that Labour “is not overrun by antisemitism, Islamophobia or other forms of racism”. She did acknowledge that “I have heard too many Jewish voices express concern that antisemitism has not been taken seriously enough” and said that there was “an occasionally toxic atmosphere”.

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One example emerged on the day Chakrabarti’s report was launched. Ruth Smeeth, a Jewish Labour MP, walked out after a party activist Marc Wadsworth accused her of working with rightwing media to attack Corbyn. She tried to complain at the time and said she received no response from the leader’s office, although Wadsworth was suspended.

(Wadsworth denies antisemitic behaviour and a party disciplinary hearing is due next month.)

Since then Smeeth said she had experienced more than 25,000 instances of abuse following that episode from the public at large, including being called a “yid cunt”. In evidence supplied to the home affairs select committee, she said that she had had to employ security at the party conference in 2016. Wadsworth, meanwhile, is fighting his suspension, and a support page dated January this year says he is a “victim of the ongoing civil war in the party” and “his ‘crime’ was to call out Ruth Smeeth”.

The subject was then given fresh impetus by activist journalist David Collier, who discovered earlier this month that Corbyn had been a member of a Facebook group called Palestine Live between 2013 and 2015, either shortly before or after he became party leader.

Some of the postings in the group were controversial, including links to Holocaust denial, allegations of Israeli involvement in 9/11 and 7/7 terror attacks and conspiracy theories involving the Rothschild family. Labour’s leader said he didn’t trawl through the group’s postings and said that had he seen any of them “I’d have challenged it straight away”.

However, with Corbyn’s social media back catalogue in focus, party backbencher Luciana Berger went back to an old story first published by the Jewish Chronicle in 2015. Her inquiry to the leader’s office for an explanation about his concerned reaction to the planned destruction of a clearly antisemitic mural in east London featuring obvious caricatures of Jewish bankers, came at a time when internal party tensions were heightened following criticisms of the leader’s response to the poisoning of the Skripals by some on the right.

Once again the leadership struggled to offer an unqualified statement. The first response to Berger’s call for an explanation was to say he was defending freedom of speech before saying the mural was offensive; a second statement said: “I sincerely regret that I did not look more closely at the image.” By then the subject of antisemitism was once again dominating coverage of Labour.

• This article was amended on 29 March 2018 to add that Marc Wadsworth denies antisemitic behaviour and that a Labour disciplinary hearing is due next month.

