Government surveillance has not kept up with sites like Twitter and Facebook, according to a former head of the UK's intelligence centre GCHQ.
Sir David Omand said criminals, terrorists and paedophiles were using social networks as a "secret space".
The government is to announce plans to plug "gaps" in how intelligence services monitor the internet.
But Sir David warned that fears over surveillance could have a "chilling effect" on the use of social media.
Government proposals to allow intelligence officers "real-time" access to emails, calls and messages without a warrant are expected to be outlined in the Queen's Speech.
But Sir David said: "We haven't had a very clear statement about how the government is approaching all this stuff."
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