A last-minute amendment to the Police Bill, tabled by the Labour front bench, proposed the establishment of specialist units with the Crown Prosecution Service and the Metropolitan Police to speed up decisions about the arrest of war criminals.

The amendment has been tabled by Shadow Police and Criminal Justice Minister Vernon Coaker and has the backing of Labour leader Ed Miliband, Shadow Home Secretary Yvette Cooper and Labour Foreign Affairs spokesman Douglas Alexander.

To date, the government has not made a final decision on the amendment, but a Conservative Party source said it looked "unattractive," as there would be serious cost implications in setting up the new bodies.

The new units would report directly to the Director of Public Prosecutions, who will sign off all warrants under the new legislation.

Under the present system, magistrates are able to issue arrest warrants for alleged war criminals. Over the past two years, several prominent Israeli politicians and military figures have cancelled visits to Britain for fear of being arrested. Israeli Opposition leader Tzipi Livni was briefly issued with a warrant in December 2009 after an application from lawyers acting on behalf of pro-Palestinian campaigners.

Conservative Party leader David Cameron said he would change the legislation on universal jurisdiction if his party came to power and the coalition has held to the pledge.

An Early Day Motion tabled by Tom Brake, who is leading on the issue for the Liberal Democrats, welcomed the DPP's assurances that he would pursue prosecutions and monitor the effectiveness of the new arrangements. Supporters of the Labour amendment argue that the new units would reassure people that the new system would not slow down the arrest of any genuine war crimes suspects. A senior Labour source told the JC that the amendment would ensure that resources were retained for the crucial work of war crimes investigations.

The proposed amendment is also designed to pacify backbenchers who are uncomfortable that the legislation could water down the principle of universal jurisdiction for crimes against humanity. But Labour figures behind the amendment were keen to emphasise that it should not be interpreted as a shift in Labour's support for Israel under Ed Miliband's leadership.

However, the amendment has caused deep consternation among some Labour supporters of Israel, who believe it is a dangerous compromise to the party's pro-Palestinian Left.

Meanwhile, the veteran Labour campaigner Ann Clwyd has proposed a wrecking amendment, to remove altogether the clause passing responsibility for war crimes arrest warrants to the DPP. This has so far been signed by 30 MPs including several prominent figures such as former higher education minister David Lammy, Green leader Caroline Lucas and Hampstead MP Glenda Jackson.