The father of murdered teenager Stephen Lawrence has warned he may not co-operate with an inquiry into police spies unless the probe is transparent.
Speaking ahead of a decision by Lord Justice Pitchford into what level of anonymity the public inquiry he heads will allow past and present officers as it probes the controversial police tactic, Neville Lawrence called for the greatest possible openness.
Asked if he would consider boycotting the investigation if it is too secretive, Mr Lawrence told BBC Radio Four's Today programme: "Yes, because we need to get to the truth, and to the bottom of what these people were doing.
"They knew this when they were taking on these jobs, that they had to do the right thing and protect the public as well as themselves, and if they go beyond where they are supposed to have gone then we have to hear and see for ourselves, and they have to give an account for doing something which is wrong.
"You can't get to the truth unless it is open to the public to hear exactly what they did. That is why we have an inquiry to make sure that they come out into public and divulge exactly what they have been doing, and what they still may be doing."
However, Mr Lawrence said he would accept some level of secrecy if revealing details would put people in danger.
Derbyshire Chief Constable Mick Creedon insisted undercover policing was a legitimate tactic which got results, and a totally open public inquiry would be "difficult".
"An over all blanket position of no anonymity would be really difficult.
"This is a lawful tactic. Without it, I'm afraid, policing would be lesser in challenging some of the biggest evils we deal with.
"Officers who work covertly as undercover officers do so at some considerable risk and they deserve our protection.
"I recognise there have been cases where their behaviour has been lacking, and it has been challenged, and what we have always done is respect the decision of the courts, and our policy of neither confirm nor deny an undercover officers identity is one which ultimately is tested by the courts.
"Clearly, if a decision is made about anonymity it is one we would respect 100%
"Whilst there have been failings in the past with undercover policing, there has also been enormous successes," Mr Creedon said.