Sweeping new laws are needed to govern the investigative powers of Britain's spying agencies, the parliamentary committee that oversees intelligence services MI5, MI6 and GCHQ has said.

Controversially, the landmark report released on Thursday by the Intelligence and Security Committee backed the right of intelligence agencies to carry out bulk interceptions of data such as emails, as well as to monitor communications between lawyers and their clients.

But it said that lawful bulk interception of data and interception of legally privileged material must be clearly enshrined within a single parliamentary act.

Finding that existing laws have not been broken, the committee said in a statement that UK intelligence agencies "do not seek to circumvent" the rules.

However, current legislation is "unnecessarily complicated," and should be replaced by a single act of parliament, concluded the committee's 149-page report — the product of an 18-month inquiry into the legal framework governing the powers of Britain's intelligence agencies.

The report also stated that agencies must be able to intercept legally privileged client-lawyer communications.

While "sympathetic" to the argument that certain professions require privacy to carry out their jobs, Britain's intelligence agencies must have the ability to intercept such communications, it said.

The committee suggested, however, that "specific professions" may justify "heightened protection" and "statutory protection should be considered."

The findings are likely to prove controversial because of the conflict of interest that could arise in cases brought against the government. An investigatory powers tribunal (IPT) case is currently looking at whether GCHQ's interception of client-lawyer communications enabled the authorities to "rig" a case brought by a Libyan rebel leader, Abdelhakim Belhaj, against Britain over its role in his rendition by the CIA to Muammar Qaddafi's jails.

The conclusion that existing laws governing the bulk interception of data have not been broken is also expected to prove controversial, because it comes a month after another landmark ruling by the IPT .

The tribunal, which hears complaints against Britain's intelligence agencies, found that regulations governing GCHQ powers breached human rights law, and that certain aspects of its operations were illegal for at least seven years.

An agreement gave GCHQ access to bulk data from the US National Security Agency (NSA)without a warrant, and an IPT ruling stated that until the legal policies governing this access were made public, these arrangements were unlawful.

The report gave a lengthy defense of any bulk interception of data, stating that it cannot be used to scrutinize an individual's communications without the authorization of the state.

"It is evident that while GCHQ's bulk interception capability may involve large numbers of emails, it does not equate to blanket surveillance, nor does it equate to indiscriminate surveillance," the committee said in a statement.

"GCHQ requires access to internet traffic through bulk interception primarily in order to uncover threats," the committee said. "Whether that might be cyber-criminals, nuclear weapons proliferators or Isil [Islamic State] terrorists.

"They need to find patterns and associations, in order to generate initial leads. This is an essential first step before the agencies can then investigate those leads through targeted interception."

GCHQ was applying extensive "targeting" and "filtering" to the data amassed, the committee said."GCHQ is not collecting or reading everyone's emails: they do not have the legal authority, the resources, or the technical capability to do so."

Senior committee member Hazel Blears said in a press statement that "limits and safeguards are essential" to the government's investigatory powers.

"In the UK, investigative action which intrudes into an individual's privacy can only be taken where it is for a lawful purpose and is determined to be necessary and proportionate.

"The question we have considered is whether the intrusion is justified and whether the safeguards are sufficient."

Cori Crider, a director at human rights charity Reprieve - whose lawyers have been representing Belhaj - said: "Once again, the ISC has been caught asleep at the wheel. It took a court case brought by Reprieve on behalf of torture victims - and significant media coverage - for the committee to become aware of a threat to the fundamental British right to a fair trial.

"State snooping on confidential lawyer-client communications carries the serious risk that court cases will be skewed in the Government's favour. Yet, due to the redactions in this report, we know nothing about what the agencies told the committee when it finally got round to calling them in for a chat."