The government must give more details on its plans for data monitoring of communications such as emails, text messages and web browsing under the proposed Communications Bill, according to a cross-party parliament panel.
The Intelligence and Security Committee (ISC) issued its report into the draft bill on Tuesday and warned that, while the need to monitor communications is vital for national security, the current Bill is too vague.
"We strongly recommend that more thought is given to the level of detail that is included in the Bill, in particular in relation to the Order-making power," it said.
"Whilst the Bill does need to be future-proofed to a certain extent, and we accept that it must not reveal operational capability, serious consideration must be given as to whether there is any room for manoeuvre on this point.
"Parliament and the public will require more information if they are to be convinced."
On the point of the Order-making power, which would grant powers to the secretary of state to require firms such as BT or Virgin Media to generate and retain communication data, it said more thought must be given to this in order to allay public fears of unnecessary monitoring.
This would relate to information including, "IP address subscriber details, data identifying which internet services or websites are being accessed; and data from overseas CSPs (communication service providers)."
However, the argument for greater monitoring powers was made by Jonathan Evans, the director general of MI5, who said accessing communication data (CD) is proving more difficult, and causing concerns.
"In general, it is becoming more difficult to be confident that you are getting CD coverage of the targets that we need to look at, and therefore from our point of view the ability to go some way at least to future-proofing our access to CD is very important," he told the ISC.
The ISC noted that while at present security services are able to get around some issues using other powers available to them, it believes the issues must be addressed.
"We believe that the decline of available communications data will begin shortly to have a serious impact on the intelligence and security agencies," it said.
The ISC noted that much of the information it gathered for its report on data gathering techniques and blind spots faced by the authorities could not be made public due to national security issues.
Opposition to the current Bill is already fierce, with numerous MPs and civil liberties groups lining up to take aim at the proposals when it was first unveiled.
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