The Commons unanimously backed a motion on Thursday night to push for a change in the law to allow intercept evidence in inquests and court hearings.
MPs said that without it there might never be an inquest into the police killing of Mark Duggan last year, which sparked riots across England.
Intercept evidence is material obtained through police snooping on someone's communications.
Labour MP David Lammy said that under the current law "we cannot know whether it is the inadmissibility of intercept evidence that would prevent an inquest being held."
The Tottenham MP's motion received support from senior Tory David Davis and Lib Dem Simon Hughes.
Mr Davis said it was an "absolute requirement" that the killing of a British citizen by state officials be properly and publicly investigated.
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