The lawyer at the forefront of the campaign to arrest Israelis for war crimes has been advising human rights organisations opposed to a reform to the universal jurisdiction law.
Daniel Machover is one of the founders of Lawyers for Palestinian Rights
The new Police and Social Responsibility Bill passes the power to issue warrants to the Director of Public Prosecutions when it previously lay with individual magistrates.
Human Rights organisations argue this will make it more difficult to pursue war criminals in this country.
A briefing document was issued last week by Human Rights Watch, legal campaigners Justice, anti-torture organisation Redress and war crimes charity Aegis as the bill reached the committee stage the House of Lords.
Electronic information contained in the document showed that it originated from Mr Machover's computer. The document proposed an amendment which would notify the DPP of any arrest warrant but not require his or her consent.
The NGOs expressed their concern that the new legislation would make it less likely for war criminals to be brought to justice.
Sally Ireland, director of Criminal Justice Policy at Justice, confirmed that Mr Machover had been consulted on the issue but said the conclusions reached were the views of the NGOs themselves: "Daniel is a recognised expert in this area. All the relevant NGOs are well known for condemning international crimes wherever they occur and in advocating that perpetrators be brought to justice and that the UK fulfils its obligations to prosecute or extradite those against whom there is evidence of involvement in such crimes."
Aegis Trust, one of the signatories to the briefing opposing the change to the law, names the Pears Foundation, one of the most generous Jewish benefactors in the country, as its founding patron.
Pears recently donated nearly £500,000 to boost Israel Studies at the School of Oriental and African Studies at London University.
Aegis is highly respected for its work on war crimes around the world and has many supporters within the Jewish community.
A Jewish Leadership Council spokesman said: "Daniel Machover is one of the most active users of the private prosecution arrest loophole that this Bill seeks to close.
"His involvement in the drafting of the NGO document calls into question its credibility."
The Police Bill continues its progress through the Lords next week.