Emily Thornberry has been criticised by a leading academic for arguing that the Balfour Declaration should be “marked” rather than celebrated, with one deeming her comments to show “a lack of socialist morality”.

Speaking on a panel that was part of the Balfour100 programme of events, Colin Shindler, emeritus professor at the School of Oriental and African Studies (SOAS), said that “if Emily Thornberry is going to be in charge of the diplomatic service, she has proved herself already to be no diplomat.”

Prof Shindler was reacting to an interview with Ms Thornberry yesterday in which the shadow foreign secretary said: “I don’t think we celebrate the Balfour Declaration but I think we have to mark it because I think it was a turning point in the history of that area, and I think probably the most important way of marking it is to recognise Palestine”.

The professor said that Ms Thornberry “reflected [Jeremy] Corbyn’s view that the Labour party has no place as a mediator. Corbyn over the last thirty years has never been a mediator between Israel and Palestine but a propagandist for one side and one side only. This goes against all the talk about peace and reconciliation – it doesn’t make any sense at all.

“She could have said: ‘The Zionists and their supporters will certainly celebrate the centenary of the Balfour Declaration. I quite understand that the Palestinians and their supporters will see it as a landmark in the history of their problems. The past can’t be changed, but the future can be; and therefore our role in the Labour party is to act as mediators between the two parties – and we’re very happy to do that.’

“That never happened, and I think it’s a lack of socialist morality on her part”. The SOAS academic was in discussion with Tim Marshall, the former foreign and diplomatic editor of Sky News, and Professor Sir Lawrence Freedman, Emeritus Professor of War Studies at Kings College London.

Mr Marshall described Ms Thornberry’s comments as “disgraceful.”

He contrasted it with words of Boris Johnson. Writing yesterday, the Foreign Secretary said: “I see no contradiction in being a friend of Israel and a believer in that country’s destiny, while also being deeply moved by the suffering of those effectively dislodged by its birth. The vital caveat of the Balfour Declaration intended to safeguard other communities has not been fully realised.”

Mr Marshall said: “Now that’s what I call even-handed and statesmanlike.” Prof Freedman rejected the argument that the Balfour Declaration had effectively triggered a 100 year conflict between the Jews and the Arabs. “The movement of Jews into Israel/Palestine didn’t start after Balfour, it was already well underway. There were already tensions, I think they would have carried on developing.

“Equally, it was a destabilising factor. I think it became more of a destabilising factor after the state [of Israel] was founded and more of a destabilising factor after the Arabs had been humiliated when they tried to crush Israel in the wars of independence, which many people thought Israel was bound to lose.”

Mr Marshall was optimistic about the possibility of peace between the Israelis and Palestinians. “If the current rate of engagement that’s been going on in the last five years [between Israel and a number of Arab countries] continues over the next five years, I think you could have enough political pressure put on both sides by the real players in the region to actually have a genuinely good stab again at a wider ‘Oslo’ – within five years. “A lot of that will be based on economics and great power politics, and the realisation that has seeped through, that the Middle East is not all about Israel and Palestine, it’s about a lot more.”

Professor Freedman revealed that, as a student, he had been attacked by Piers Corbyn, the Labour leader’s brother. “One of my early political experiences was being denounced as a Zionist by Jeremy Corbyn’s brother Piers when I was trying to go for an office in the National Union of Students”, he said. “I’d never even been to Israel at that point.”

The event, held at a sold out JW3 Jewish community centre in north west London, was organised by the JC.