Witnesses in a public inquiry into secret police tactics should be able to give evidence without incriminating themselves, its chairman has said.
The information they provide should not be used against them - or their spouse or civil partner - in any criminal investigations afterwards, Lord Justice Pitchford said.
His ruling, which will be presented to the Attorney General, aims to remove any fear those giving evidence may have about facing prosecution on the basis of what they say at the inquiry, he said.
The same rule would not apply to evidence given by other people, Sir Christopher Pitchford's ruling states, leaving open the possibility of a witness being prosecuted following information given by another witness.
He said: "I will not request the Attorney General at this stage to consider giving an extended undertaking in the terms sought by the non-police, non-state co-operating group. But I will keep this issue under review and will not dismiss the prospect of such a request altogether."
Home Secretary Theresa May announced the inquiry into undercover policing in England and Wales in 2015 after a series of claims about Scotland Yard's secretive Special Demonstration Squad (SDS), which operated between 1968 and 2008.