Sir David Omand - Social media snooping powers out of date
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."Centre of excellence
A report co-written by Sir David for think tank Demos found that intelligence gathered from blogs, Twitter and Facebook should be "collected and used in a way that is both effective and ethical".
"For safety and security, authorities have got to be able to tackle this kind of space," Sir David said.
"I don't know anyone who would say that you should ring-fence social media and say 'that's a secret space where paedophiles, criminals and terrorists can happily play because you can't get at it'."
Demos said the government should consult on "how it plans to use and manage" social media intelligence "in the public interest", and should establish a "centre of excellence" to co-ordinate social media intelligence policy and funding.
But the reports' authors said an "open" internet that promotes the "free exchange of ideas" was an economic and public good and should be protected under any new regulation.
They said that future intelligence gathering must be based "on respect for human rights and the associated principles of accountability, proportionality and necessity".
Without that, there is a "danger that [it] could result in a chilling effect on the use of social media itself, which would have negative economic and social consequences for the country as a whole".
Social media could help the intelligence community and the police identify criminals, give early warnings before public order incidents, and help them "understand and respond to public concerns", the report found.
The report's authors argue this approach would have helped the police deal with last August's riots, when Blackberry messaging was blamed by some for allowing rioters to coordinate their activities.Bugging
They argue the security services and the police should monitor publicly available information on sites like Twitter and Facebook during demonstrations or riots.
This would enable them to "gain situational awareness" and gauge "levels of community tension" while respecting users' anonymity, they said.
But ethical and legal guidelines are needed to regulate the use of more intrusive monitoring, which would involve accessing personal information - ignoring users' privacy settings - as well as emails and messages.
Sir David said accessing private Blackberry messages would be the modern equivalent of bugging a personal telephone call and should require a warrant.
According to the Demos report, around 40% of people in the UK feel the police should be able to access information on social networking sites when investigating crime.
The authors argue such surveillance should be a last resort, proportional, and carried out with proper oversight where there is a "reasonable prospect of success".
A Home Office spokesman said: "Communications data, the who, when and where of a communication, has played a role in every major security service counter-terrorism operation over the past decade.
"Interception of the content of a communication is only possible with a warrant signed by the secretary of state and we have no plans to change this."