The UK government's plan to allow "thematic warrants" under its Investigatory Powers Bill is "too broadly drafted," MPs and peers sitting on parliament's human rights joint committee have concluded.

In its report, the committee has recommended amendments to the bill so that the description of the warrant is "sufficiently specific to enable the person unknown, but who is the subject of it, to be identified and to prevent the possibility of large numbers of people being potentially within the scope of a vaguely worded warrant." The current draft of the IPB allows for thematic snooping warrants that can be used against whole groups or classes of people.

The panel appeared to be less worried about the IP bill's "bulk powers," however, which it believes are "not inherently incompatible with the right to respect for private life, but are capable of being justified if they have a sufficiently clear legal basis, are shown to be necessary, and are proportionate in that they are accompanied by adequate safeguards against arbitrariness."

It calls for the operational case for bulk powers to be assessed by the independent reviewer of terrorism legislation—something which home secretary Theresa May recently agreed to do. Though it's worth noting that the assessment's terms of reference are yet to be published.

The committee also noted that there is currently a case before the Court of Justice of the European Union which will consider whether the UK's approach to bulk surveillance is allowed under EU law—its outcome could have a dramatic impact on the Snoopers' Charter.

The proposed power to make major modifications to warrants for targeted interception has raised concern among the committee. As its report pointed out, this ability is "so wide as to give rise to real concern that the requirement of judicial authorisation can be circumvented, thereby undermining that important safeguard against arbitrariness." To address that problem, the committee recommended that big changes to warrants should be approved by a judicial commissioner.

The report also demanded the legal protection for three kinds of communications to be tightened up: those involving MPs and their constituents; between lawyers and their clients, and for journalists communicating with sources.

Finally, it calls for oversight of the powers regulated by the Snoopers' Charter to be strengthened. It suggests creating a separate system for reviewing authorisations alongside the one that issues warrants in the first place.

Despite these issues, the joint committee generally welcomed May's draft legislation, calling it "a significant step forward in human rights terms towards the objective of providing a clear and transparent legal basis for the investigatory powers already being exercised by the security and intelligence agencies and law enforcement authorities and, in many respects, enhanced safeguards."

The main issue to emerge from the report is the problematic nature of the thematic warrants, which are currently almost unlimited in their reach and power. Coupled with similar criticisms from parliament's intelligence and security committee, this is likely to be an area that comes under particular scrutiny when the bill returns to parliament next week for its report stage and third reading.