On 27 December last year, Israel launched Operation Cast Lead in Gaza, an overwhelming exercise of military force aimed at silencing the Hamas rockets which had terrorised Israeli towns and villages. The immediate effects of the invasion are well known: 1,400 Palestinians dead, mostly civilians, with many more wounded or displaced; 10 Israeli soldiers and three civilians killed, dozens more injured; and thousands of families in southern Israel forced to flee to other parts of the country. The rocketfire from Gaza into Israel has slowed but has not entirely ceased. Hamas is still in power.

What is less well-known is the escalating humanitarian crisis in Gaza. The legacy of Operation Cast Lead is a living nightmare for one and a half million Palestinians squeezed into one of the most overcrowded and wretched stretches of land on the planet. And as Israel and Egypt maintain a near total blockade against Gaza, the misery deepens by the day.

This is not only shocking in humanitarian terms. It is not in Israel's or Egypt's interest, either. Confining people in abject poverty in a tiny slice of territory is a recipe for continued bitterness, fury and radicalism.

And what has the British government and the international community done to lift the blockade? Next to nothing. Tough-sounding declarations are issued at regular intervals but little real pressure is applied. It is a scandal that the international community has sat on its hands in the face of this unfolding crisis.

No doubt the febrile sensitivities of the Middle East have deterred governments, caught between recriminations from both sides. No doubt diplomats have warned that exerting pressure on Israel and Egypt may complicate the peace process.

But surely the consequences of not lifting the blockade are far more grave? How is the peace process served by sickness, mortality rates, mental trauma and malnutrition increasing in Gaza? Is it not in Israel's enlightened self-interest to relieve the humanitarian suffering?

The peace process is in serious trouble right now. Internal Israeli politics limits any meaningful room for manoeuvre, illegal settlement activity in the West Bank continues, and leadership of the Palestinians is divided and incoherent. A two-state solution, long the accepted bedrock of any agreement, is being openly questioned.

But paralysis in the peace process cannot be an excuse for the inhumane treatment of one and a half million people, the majority of them under 18 years old. No peaceful coexistence of any kind is possible as long as this act of collective confinement continues.

According to a recently leaked report by the UN office of the humanitarian co-ordinator, Gaza is undergoing "a process of de-development, which potentially could lead to the complete breakdown of public infrastructure". A report released today by a group of 16 humanitarian and human rights groups further spells out the effects.

Family homes destroyed in the invasion lie as shattered as ever. The embargo on construction materials means they will stay that way. Local hospitals and clinics were left devastated by the invasion, and those suffering health problems wait longer than ever to get out of Gaza for treatment. Many have died waiting. Bed-wetting and nightmares are endemic among children.

Half of those under 30 are unemployed. These young people are trapped in a broken land with little hope of economic opportunity. The blockade's restrictions on Gaza's fishermen mean they can sail only three nautical miles from the coast, impoverishing their families. Meanwhile, 80m litres of raw and partially treated sewage is pumped out into the sea every day.

Most disturbingly of all, the lack of access to materials means that basic water infrastructure simply cannot be repaired or improved; 90 to 95% of Gaza's water fails to meet WHO standards. The extremely high nitrate level in the water supply is leaving thousands of newborn babies at risk of poisoning.

The insistence by some that aid should come into no contact whatsoever, even indirectly, with Hamas means NGOs are prevented from repairing basic water and sanitation facilities in schools.

There is a clear moral imperative for Israel and Egypt to end the blockade, as well as it being in their enlightened self-interest to change course. But if they do not do so of their own volition, it is up to the international community to persuade them otherwise.

The EU has huge economic influence over Israel, and it believes the blockade must be lifted. At the same time as exercising leverage over Hamas, it should make clear that the web of preferential agreements which now exists between the EU and Israel – from Israeli access to EU research and development funds to recently improved access for Israeli agricultural products – will be brought into question if there is no rapid progress.

Equally, the US, as by far the largest bilateral donor to Egypt, should press President Mubarak to allow in the humanitarian and reconstruction materials that are so desperately needed.

What will be the state of Gaza's drinking water by next December? Of the health of its children? Of the economy? The attitude of its people towards Egypt and Israel? The risk of waiting another year is too great. Gordon Brown and the international community must urgently declare that enough is enough. The blockade must end.