A key figure behind Jeremy Corbyn’s rise to become Labour leader has said that some on Britain’s left are in denial about the impact of certain pro-Palestinian slogans on Jewish people. Jon Lansman, the founder of the grassroots movement Momentum, said he and others had come to feel alienated by Britain’s main pro-Palestinian campaign and revealed he had recently joined the Jewish Labour Movement (JLM), the party’s oldest Jewish affiliate and one that was highly critical of Corbyn. Lansman also challenged Keir Starmer to sign a new joint letter from a range of Jewish and Arab social justice groups and others calling for a “a stable ceasefire” between Israel and Hamas, along with a commitment to negotiations, mutual recognition of rights to self-determination and an end to settler violence and the harming of innocent civilians. He spoke of the impact on leftwing Jews such as himself when they had taken part in protests by the Palestine Solidarity Campaign (PSC) and heard the contested chant: “From the river to the sea, Palestine will be free.” The phrase, regarded by some as a legitimate expression of support for Palestinian statehood but by others as advocating the eradication of Israel, has increasingly been questioned since the Hamas atrocities of 7 October. “Most people who go on PSC marches are people who genuinely want to express solidarity with the Palestinian people and I have no problem with that,” Lansman said. “But in the past – the last time I was on one was 2015 or 2016 – I found it uncomfortable to hear the ‘from the river to the sea Palestine will be free’ chant. Where does does it leave Israeli people? Can there not be scope for a message that has the sentiment ‘from the river to the sea Palestinians and Israelis shall be free and equal’?” He said it was also “unhelpful” that some in the leadership of the PSC, which was behind Saturday’s march in the centre of London, appeared to be only in favour of a “one-state” resolution. Lansman spoke to the Guardian at a time when many leftwingers from a Jewish background have challenged what they saw as shortcomings in the reaction of erstwhile comrades on the British left to the Hamas attacks. After the atrocities, dozens of left-of-centre Israeli academics published an open letter criticising political allies abroad for their “inadequate response” to the attacks. Lansman, 66, who was brought up in an Orthodox Jewish family, worked on an Israeli kibbutz in his teens and has maintained links with Israeli’s left, was also critical of the way in which Jews have come to be characterised on the left. “One of the problems is that many on the left insufficiently differentiate between Jews. They seem to categorise them as Zionists or anti-Zionists,” he said. “In fact, British Jews have a wide range of views and very many who the left might see as ‘Zionists’ are critical of illegal settlements, the occupation, of the Israeli government and even of the conduct of the present war.” Like others, he said he now found himself conflicted against the backdrop of the current conflict. While recoiling from the particular horror of the Hamas attacks, he added: “There are similarities between Hamas and ministers from the [far-right] Religious Zionist party in the Israeli government that are horrible.” As for tensions that have embroiled Keir Starmer over whether to call for a ceasefire, Lansman said he had some sympathy – though he said he was not opposed to calling for a ceasefire to facilitate humanitarian relief or pave the way for a settlement based on peace and security. “I want a cessation as soon as possible but my view is that a ceasefire without a clear purpose will not change the tide of the war and could just end up making it go on for longer,” he said in an interview last week. “As it happens I have some sympathy for Keir Starmer’s conclusion that calling for a ceasefire now is wrong. A ceasefire now could merely sustain Hamas as a continuing threat.”
 He had turned towards what practical contribution he and others could make to peace in the medium to long term, suggesting that there could be a campaign to free younger Palestinian prisoners in Israeli jails as a way of creating alternatives to the unpopular figures in control of the Palestinian Authority (PA). “Both Jews and Palestinians have been poorly served by their current leaders and need new ones to provide partners for peace,” he said.