The idea that armies should use proportionate force was dismissed by a former director of military intelligence for the Israel Defence Forces at a special session on Gaza at the Limmud conference.

General Yaacov Amidror said: “The advantage Israel has, is only because it can react disproportionately.”

From a military perspective, he added: “The only way to deal with such a situation is to react without taking into consideration proportionality… otherwise you will lose before you begin.”

One of the conference venue’s largest lecture theatres was packed, with some having to sit on the stairs, for the hastily convened panel discussion. Questions from the floor indicated a desire to seek information more than to express a view of Israel’s actions.

General Amidror, arguing that the use of group troops would be necessary, warned that civilian casualties would increase as they did as the IDF provided its soldiers with covering fire.

David Newman, professor of geopolitics at Ben Gurion University, who said he was unsure whether Israel’s response was correct but that it posed an ethical dilemma, nonetheless agreed that “discussion of proportionality is a farce”. He said: “You use your strength to win a war.”

But Daniel Taub, deputy legal adviser in Israel’s Foreign Ministry, argued: “International law is not a suicide pact. It doesn’t require you to take measures that will necessarily end in failure.”

If Israel stopped being guided by international legal principles, it was likely to lose both international support and the moral ground, he said.

But he reminded his audience: “A military target does not stop being a military target if it’s a lawful military target simply because the people on the other side have placed in the heart of a civilian area.”

In the Lebanon war, legal advisers had even been in the bunkers with military commanders to advise on targetting. But when Mr Taub said that the Winograd Commission had later questioned whether such steps were appropriate during war, General Amidror loudly chipped in, “No.”

Ali Abu Awwad, co-founder of the Palestinian peace movement Al-Tariq, who proved to be one of the conference favourites, said that violence could not produce freedom or security, only “more broken hearts”.

Mr Taub, though saying that he disagreed with Mr Abu Awwad over some things, paid tribute to his “unbelievable courage and desire for peace that he has expressed.”

Gerald Steinberg, political scientist from Bar-Ilan University, said that international criticism of Israel had so far generally been lower than in the Lebanon War and “the BBC has been somewhat more even-handed.”

But he described a cartoon in The Independent newspaper showing Ehud Olmert bathing in blood as “antisemitic”.