One of the values enshrined in the code of the Israeli Defense Forces (IDF) is that its soldiers will behave with scrupulous morality, even in the heat of combat. So the testimony published in a college newsletter from some Israeli soldiers who served in the recent military engagement in Gaza will come as a severe shock to a public taught to trust in its army's "purity of arms".

What these soldiers describe from their experience of the three-week long Operation Cast Lead is not scrupulous morality, but an almost complete absence of it. They cite wanton destruction of Palestinian property and a chilling indifference to civilian casualties. They also relate how such abuses were made possible by the permissive rules of engagement established by their superiors.

This is not the first time allegations of possible war crimes by Israeli soldiers during the Gaza operation have been made. Until now the IDF has shrugged off such claims, accusing those human rights groups which related tales of illegal killing and destruction of either being duped by Hamas or pursuing their own anti-Israeli agenda.

But that avenue is not open to the army on this occasion. This testimony cannot be dismissed as enemy propaganda because it comes from a respected Israeli college. And the soldiers themselves have no reason to lie about what they saw, and, in some cases, carried out. The question is how Israel itself will respond to such incendiary testimony; with a resolve to get to the truth, or denial?

It is true that all armies suffer occasional breakdowns in discipline. And we should not make the mistake of holding Israeli soldiers to a higher standard of conduct than we expect from our own. We in Britain should remember that Baha Mousa, an Iraqi hotel receptionist, was beaten to death in the custody of British troops in Basra in 2003 and none of our soldiers was convicted of this killing. American military personnel were guilty of appalling abuses of prisoners in Baghdad's Abu Ghraib prison.

We should bear in mind too that this testimony was made public by a concerned Israeli academic. Whatever crimes might be laid at the door of the IDF, it should not be Israeli society on trial here. Indeed, it is a tribute to the openness of Israel's democracy, that we have learned of these allegations. Nor does the conduct of Israeli troops invalidate the overall objective of Operation Cast Lead, namely to stop Hamas firing rockets into towns in southern Israel.

All this is true. Yet none of it excuses what has apparently happened in Gaza. It is vital that the Israeli government should investigate these allegations and do so openly. The process should certainly not be left in the hands of the IDF.

The army's failure to investigate previous allegations of misconduct by its troops in a serious fashion leaves no confidence that it is about to change its ways now. An outside investigator should also look into the IDF's distribution to soldiers of a pamphlet containing vile religious extremism prior to the Gaza invasion.

The strength of Israel is measured not only in the sophistication of its military technology, but in the openness of its society and the clarity of its values. If Israel fails to root out the canker of brutality and ill-discipline from the IDF, it will deal itself a heavier blow than any of its enemies in Hamas or Hizbollah have thus far managed to inflict.