As Tamils across gathered across the world last week to remember and mourn the Vanni slaughter of May 2009, the growing movement for an internationally mandated mechanism to account for the war crimes and crimes against humanity that took place during Sri Lanka's military onslaught against the LTTE also arrived at an important landmark.

On the 17th of May the International Crisis Group published a report detailing allegations of war crimes committed during the final months of the war and made a compelling case for an international mechanism as the only viable means of realizing accountability and justice.

The report captures important changes in the international politics of Sri Lanka which must increasingly shape British engagement with Sri Lanka and the new coalition government's efforts to support peace, stability and development on the island.

Specifically the ICG establishes that in the final months of the war the Sri Lankan military herded civilians into free fire zones and then wantonly shelled and bombed them with the explicit purpose of destroying Tamil civilian life.

In demanding an international rather than Sri Lankan mechanism of justice, the ICG has joined the growing chorus of Tamil and international voices insisting that the Sri Lankan legal system is institutionally incapable of establishing accountability and the rule of law, essential to securing political stability on the island.

It is now clear that the time for 'quite diplomacy' in dealing with Sri Lanka's spiralling political crisis is now past. Unless there is concerted international action, Sri Lanka's conflict will only escalate, even if the war is over.

The report adds momentum to British Tamils' calls for a new departure in Britain's approach to Sri Lanka. British support for development on the island can no longer ignore Sri Lanka's brutality towards the Tamils.

While it is now undeniable that Sri Lanka's treatment of the Tamils amounts to war crimes and crimes against humanity, there is mounting and credible evidence that Sri Lanka is also guilty of the more urgent crime of committing genocide against the Tamil population on the island.

At a minimum level British policy should now be re-orientated to include explicit and practical support for international initiatives on the war crimes issue. There is already an infrastructure in place for this. The Home Office has an established War Crimes Unit. Until now the unit has focussed its attention on the LTTE. It has spent its time and resources in marshalling unreliable evidence from partisan Sri Lankan sources such as the Colombo based University Teachers for Human Rights in usually failed efforts to deport or prosecute alleged LTTE members.

Tamil activists can now make a credible case to politicians and policy makers demanding that the unit focuses its attention on the more pressing issue of the war crimes committed during the final months of the war. The Unit must support efforts to collect evidence from sources within Britain and also investigate the possible routes through British and international law to bring the perpetrators to justice.

There are a wealth of sources within the British Tamil community who can give reliable and detailed evidence of the events that took place in the final months of the war. The War Crimes Unit can also easily marshal evidence on the abuses that occurred, and continue to occur, in Sri Lanka's squalid detention camps.

After the shelling finally stopped, many British Tamils made frantic efforts to contact their friends and relatives who had been in the Vanni. There are innumerable stories of extortion, rape and physical abuse. The Home Office Unit has an international and domestic responsibility to collect and document this evidence.

At a broader level Britain must also lead efforts to place the war crimes issue in a wider political context. Sri Lanka's military onslaught in the Vanni was an attempt to militarily resolve the Tamil question. A resolute and international approach to the war crimes issue has to be coupled with an equally resolute and international approach to the Tamil question.

Just as Sri Lanka's legal system is unwilling to deliver justice and accountability, Sri Lanka's political class is also unwilling to recognise and guarantee Tamil political rights. The Tamil issue will only be resolved when the international community collectively adopts a commitment to the recognition of Tamil political rights when dealing with Sri Lanka.

A year after the end of Sri Lanka's attempted military solution to the Tamil question, there has undeniable progress towards establishing a new and more productive international approach to Sri Lanka's crisis. The ICG report is an important landmark in the changing international politics of Sri Lanka.

British Tamils must work to ensure that British policy is re-orientated to be in line with the shifting international climate. There are immediate practical steps that can be taken on the collection and documentation of war crimes evidence. At a deeper level Britain alongside the rest of the international community must make the recognition of Tamil political rights a central component of resolving Sri Lanka's political crisis.