Under Article 51 of the UN Charter, a state can take military action without the prior authorisation of the Security Council if it is acting in self-defence. Yet, as CNN has reported, it was Israel – and not Hamas fighters – that broke the ceasefire. On the November 4 2008, Israel shelled the villages of Wadi al-Salqa and al-Qarara, killing six Hamas activists.

It is true that Israel has suffered from Hamas rocket attacks. Insofar as these attacks indiscriminately target civilian areas, Hamas would be guilty of war crimes under the Geneva Conventions of 1949. Yet, in the past eight years, Palestinian rockets fired from Gaza have killed around 20 people in southern Israel. Israel's response is neither necessary nor proportionate.

At the time of writing, after 23 days of bombardment, more than 1,300 Palestinians have been killed by Israel, including 410 children and 104 women, while 5,300 are seriously injured, of whom 1,855 are children and 795 women. Israel has shelled three clearly marked UN schools, the existence and GPS coordinates of which Israel had been repeatedly notified. Israel has shelled the headquarters of UNRWA, the UN's relief agency (which is responsible with providing aid to 750,000 Palestinians), and it has shelled and bombed hospitals, ambulances, and medical personnel. In typical Israeli fashion, it has bulldozed homes without warning in an attempt to bury the inhabitants alive. Recent UN human rights reports expose that the Israeli army has deliberately used white phosphorus on civilians, which is prohibited "in all circumstances" under Protocol III of the Convention on Conventional Weapons, and evidence has emerged that Israeli snipers have deliberately targeted civilians.

On January 4, Israeli soldiers evacuated approximately 110 Palestinians into a single-residence house in Zeitoun and warned them to stay indoors. Half of the evacuees were children. Twenty-four hours later, Israeli forces shelled the home repeatedly, killing 30 of the inhabitants, although more bodies are likely to be recovered from the ruins.

After several days of requesting safe passage to the area, on January 7, during a three-hour lull in hostilities, an ICRC medical team was finally allowed in on foot (without ambulances) into the closed military area to evacuate any remaining survivors. According to testimonies gathered by the UN, Palestinian children were left unable to walk or speak, in shock and weeping by the bodies of their dead mothers. When the IDF finally let through the International Committee of the Red Cross, the children were led from the building past dogs eating the corpses of the victims.

Navi Pillay, the UN high commissioner for human rights and a former international criminal court judge from South Africa, has stated that the incident in Zeitoun "appears to have all the elements of war crimes". Israel has not ratified the 1998 Rome Statute, so its leaders cannot be brought before the International Criminal Court in the Hague, unless the UN security council itself refers Israel's actions to the ICC. The US abstained from the recent UN security council resolution calling for a ceasefire, and it would almost certainly wield its powers as a permanent member of the security council to veto any attempt to refer Israeli leaders to the ICC.

In UK law, the Geneva Conventions Act 1957 and the Geneva Conventions (Amendment) Act 1995 attempt to afford the domestic courts universal jurisdiction for "grave breaches" of humanitarian law. This includes wilful killing, torture or inhuman treatment, wilfully causing great suffering or serious injury to body or health, extensive destruction and appropriation of property, which was not justified by military necessity and was carried out unlawfully and wantonly. Attacks on the wounded, the sick, or against medical units and personnel also constitute grave breaches, as does making the civilian population the object of attack practices of apartheid and other inhuman and degrading practices involving outrages upon personal dignity, based on racial discrimination.

On September 10 2005, the chief London magistrate Timothy Workman issued a warrant for the arrest of the retired Israeli Major General Doron Almog, in relation to the wanton destruction of 59 houses in Rafah refugee camp on January 10 2002. After Almog had landed at Heathrow, he was tipped off and he flew back to Israel. Perversely, the attempt to bring Almog to justice for war crimes caused the then foreign secretary, Jack Straw, to apologise to his Israeli counterpart for the attempted arrest. As Arthur Neslen has observed, it would seem that war crimes are fine, so long as someone says sorry afterwards.

Palestinians are living under occupation, and are therefore "protected persons" under the Fourth Geneva Convention of 1949. Protected persons may not be punished for crimes that they themselves have not committed, and their collective punishment constitutes a war crime.

Israel's attempt to claim self-defence as a justification for the separation wall, which annexes swathes of Palestinian land, has already been rejected by the International Court of Justice. On July 9 2004, the International Court of Justice provided its advisory opinion that the construction of the wall is contrary to international law and that Israel was obliged to dismantle the wall forthwith. The court rejected Israel's defence that the separation wall is justified under the doctrine of self-defence under Article 51 of the UN Charter.

When the Middle East envoy for the Quartet, former UK prime minister Tony Blair, was interviewed by Gavin Esler on BBC Newsnight on January 9, he opined that a ceasefire had not been possible because: "I think that there are still real issues about what can be done to stop the smuggling of the arms going into Gaza and then the opening of the crossings so that there can be proper humanitarian help." Blair effectively makes the Palestinians' right to humanitarian aid dependent upon whether their democratically elected leadership can be prevented from bringing arms into Gaza.

Yet, as Article 55 of the Fourth Geneva Convention states: "To the fullest extent of the means available to it, the Occupying Power has the duty of ensuring the food and medical supplies of the population; it should, in particular, bring in the necessary foodstuffs, medical stores and other articles if the resources of the occupied territory are inadequate." It would appear that Blair regards international law as either irrelevant or a hindrance.

Despite the Israeli supreme court's recent ruling in favour of the petitioner, the Foreign Press Association, that foreign journalists must be allowed into Gaza, the Israeli state prevented proper access throughout its attack. As the FPA's lawyer, Gilead Sher, observed: "There are several countries in this world, such as North Korea, Zimbabwe and Burma, that ban press coverage in conflict zones." Israel must ask itself whether this is really the company it wants to keep.