Britain is playing a key role in efforts to block the prosecution of Sudanese President Omar al-Bashir for the carnage in Darfur.

Human rights activists yesterday accused the government of a 'shocking abdication' of its commitment to justice after it emerged that Britain is backing moves by Libya, the Arab League and several African countries to halt the indictment of Bashir by the International Criminal Court (ICC) in The Hague.

But the government says it has adopted the controversial position to save lives in the western Sudan province where the United Nations estimates that 200,000 people have died and 2.5 million others have been driven from their homes since 2003.

In July the ICC's chief prosecutor, Luis Moreno-Ocampo, applied for an international arrest warrant for Bashir - the first such move ever against a serving head of state. The prosecutor wants to try Bashir for genocide, crimes against humanity and war crimes. He claims to have evidence that the Sudanese state and its agents have killed at least 135,000 people in Darfur. The move was criticised by some regional experts, who argued that it would bring greater suffering and threaten hopes of a peace deal.

Britain was a leading player in the establishment in 2002 of the ICC - a unique permanent court with wide-ranging powers and a UN mandate to end impunity at high levels and punish war crimes, including genocide.

In a last-ditch attempt to prevent ICC judges from issuing an arrest warrant for Bashir in the next few weeks, Bashir's supporters - the Arab League, the African Union, China and Russia - will use the UN General Assembly, beginning on 23 September, to ask the UN Security Council to block the prosecution. They are supported by two countries which were instrumental in instigating the ICC investigation - permanent Security Council members Britain and France.

Britain and France say privately that the lines of communication with Khartoum are nearing total breakdown. The Sudanese authorities are blocking the work of the 11,000-strong Unamid peacekeeping force and have not handed over two other ICC suspects - government minister Ahmad Harun and militia chief Ali Kushayb - for whom arrest warrants were issued last year.

Foreign Office Minister for Africa Mark Malloch Brown and his French counterpart, Bruno Joubert, are understood to have both travelled to Khartoum recently to suggest a deal under which Bashir could be let off the hook. It would require Khartoum handing over Harun and Kushayb, committing to the peace process in Darfur and southern Sudan, and allowing Unamid to fully deploy.

But Steve Crawshaw of Human Rights Watch said bargaining with justice will permanently undermine the ICC's credibility and independence. 'The idea that you can do deals on justice is both short-sighted and a shocking moral abdication on Britain's part. It can only be damaging to the court.

'Justice is not a tradeable option. We have seen again and again that Sudan makes empty promises. To think that Sudan is likely to act in good faith is either naive or cynical,' said Crawshaw.

The ICC prosecutor is confident of his case. His special adviser, Beatrice Le Frapper, said: 'We share the objective of stopping the crimes in Darfur. But to do so you need justice and security. Unamid will not be able to carry out their tasks if they have to liaise with criminals who are ordering crimes against civilians. The indictment of Bashir contributes towards his becoming a lame-duck President.' She said the ICC would meet Foreign Secretary David Miliband and his French counterpart, Bernard Kouchner, to outline the ICC's position on 23 September.

But Malloch Brown defended Britain's role: 'It is precisely because we respect the ICC that we do not want to bargain away (its authority). This is not about handing a defeat to the court in its early life. But Khartoum has interpreted the indictment against Bashir as a measure that pits Sudan against the Western world. A great deal is at stake; not just Darfur but the peace process in southern Sudan. We have to keep hold of the strategic intentions of the ICC, which we share - to end impunity and increase security in Darfur.'