Rt Hon Keith Vaz, chair of the Home Affairs Select Committee, has called for a "clear code of conduct" for police officers operating undercover.
He told ITV News that cases of undercover police officers fathering children with their subjects, or using the identities of children who have died, were "abhorrent".
"This isn't James Bond, this is happening," he added.
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ITV Border Political Editor Peter MacMahon says it's far too early to call this referendum.
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