Conservatives are among MPs battling to stop the government granting immunity to British ministers, spies and military personnel for involvement in murder and torture abroad.
Tory grandee David Davis is bringing a series of amendments to the National Security Bill, which has alarmed human rights groups and anti-war crime campaigners.
The proposed changes, aiming to strip out clauses granting legal immunity and restricting damages for torture survivors, will be debated in the House of Commons later on Wednesday.
In a move backed by the former justice secretary Robert Buckland, opposition MPs are also attempting to add a public interest defence into the Official Secrets Act to protect whistleblowers and journalists.
In a letter to the prime minister, a group of charities including Reprieve, Liberty, Amnesty International UK and Freedom From Torture questioned why the government would “seek to protect themselves and their officials” from prosecution for assisting or encouraging crimes abroad.
“It is unconscionable that the British government might shield ministers or officials from accountability,” the letter said.
“With no limits on what criminal activity the clause includes, this provision could be used to shield British ministers and officials from prosecution where they have encouraged or assisted extraordinary rendition, interrogations involving torture, or unlawful targeted killings.”
The bill would grant immunity against prosecution in Britain if the conduct was “necessary for the proper exercise of any function of the Security Service (MI5), the Secret Intelligence Service (MI6) or GCHQ”, or the armed forces.
Human rights campaigners cited unresolved cases where the UK was accused of providing information leading to torture, including that of Jagtar Singh Johal, who was detained in India after speaking out against abuses against the Sikh community.
Separate provisions would make judges reduce the compensation awarded in civil cases against the government, such as to torture victims, if there were “national security factors” including links to terrorism.
Former Conservative minister Mr Davis is bringing amendments, backed by opposition MPs, to remove the clauses on immunity from prosecution and changes to compensation arrangements.
He and Mr Buckland, the former justice secretary, are among MPs supporting a Labour amendment creating a public interest defence to the Official Secrets Act, in order to protect whistleblowers and journalists.
The Society of Editors, which represents British newspapers, said the bill “poses a grave threat to press freedom” and rides roughshod over established protections.
It said that the government’s changes could criminalise public interest journalism and silence whistleblowers.
Dawn Alford, executive director of the Society of Editors said: “Despite widespread consensus as to the absolute necessity of a public interest defence, it remains baffling as to why the government has chosen to omit one.
“Such a defence is backed by both the Law Commission and Parliament’s Joint Committee on Human Rights and, without it, there are no adequate protections to ensure that those that bring information that is demonstrably in the public interest into the public domain are free from the threat of lengthy jail terms and prosecution.”
Groups including Index on Censorship and Reporters Without Borders are also calling for a public interest defence.
When bringing forward the wide-ranging National Security Bill in May, Priti Patel said it would “protect the country from hostile foreign activity whether abroad or on our soil”.
The former home secretary said the legal framework governing the intelligence services needed to be updated, hailing the Foreign Influence Registration Scheme contained in the package of laws.
“It will also allow intervention in state threats activity much earlier, by criminalising conduct in preparation for state threats activity meaning that arrests can be made at an earlier stage before damage is done,” she added.
