All police forces in the country will be made to examine their archives to search for evidence of misconduct by undercover officers following allegations surrounding the Stephen Lawrence murder inquiry.
Policing minister Damian Green admitted the probe could lead to "some very unpalatable truths" coming out, but said it was better than keeping them hidden.
He is expected to tell the chief constables of the 43 forces in England and Wales they must carry out the searches following the revelation that an undercover officer was told to find information to use to smear the Lawrence family after the teenager's racially aggravated murder in 1993.
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