British intelligence services can access raw material collected in bulk by the NSA and other foreign spy agencies without a warrant, the government has confirmed for the first time.

GCHQ’s secret “arrangements” for accessing bulk material are revealed in documents submitted to the Investigatory Powers Tribunal, the UK surveillance watchdog, in response to a joint legal challenge by Privacy International, Liberty and Amnesty International. The legal action was launched in the wake of the Edward Snowden revelations published by the Guardian and other news organisations last year.

The government’s submission discloses that the UK can obtain “unselected” – meaning unanalysed, or raw intelligence – information from overseas partners without a warrant if it was “not technically feasible” to obtain the communications under a warrant and if it is “necessary and proportionate” for the intelligence agencies to obtain that information.

The rules essentially permit bulk collection of material, which can include communications of UK citizens, provided the request does not amount to “deliberate circumvention” of the Regulation of Investigatory Powers Act (Ripa), which governs much of the UK’s surveillance activities.

This point – that GCHQ does not regard warrants as necessary in all cases – is explicitly spelled out in the document. “[A] Ripa interception warrant is not as a matter of law required in all cases in which unanalysed intercepted communications might be sought from a foreign government,” it states. The rules also cover communicationsdata sent unsolicited to the UK agencies.

Campaigners say that this contrasts with assurances by parliament’s Intelligence and Security Committee in July last year that a warrant signed by a minister was in place whenever GCHQ obtained intelligence from the US.

The data can then be stored for up to two years, the same duration as information collected directly by the agency. This can be extended unilaterally if a senior official believes it to be necessary and proportionate for national security purposes.

Privacy International, one of several advocacy groups mounting legal challenges against GCHQ and NSA surveillance, said the revelation should cast further doubts on legal safeguards in the UK.

“We now know that data from any call, internet search, or website you visited over the past two years could be stored in GCHQ’s database and analysed at will, all without a warrant to collect it in the first place,” said deputy director Eric King. “It is outrageous that the government thinks mass surveillance, justified by secret “arrangements” that allow for vast and unrestrained receipt and analysis of foreign intelligence material is lawful.”

The group also said information obtained through these overseas “arrangements” was treated as if it were targeted surveillance, removing a requirement under UK law not to search for UK citizens and residents in such data troves. This means that British citizens could, in theory, be subject to warrantless monitoring by GCHQ.

Amnesty International and Liberty, the co-complainants in the IPT case, echoed Privacy International’s call for reform of surveillance safeguards.

“It is time the government comes clean on such crucial issues for people’s privacy as the sharing of communications intercepts with foreign governments,” said Amnesty International director of law and policy Mike Bochenek. “Secret rules are woefully inadequate.”

Liberty’s legal director James Welsh said the tribunal submissions contradicted public statements from the government.

“The line the Government took at the hearing was that there were adequate safeguards, they just couldn’t be made public,” he said. “Leaving aside whether secret safeguards can ever be adequate, this reluctantly-made disclosure suggests otherwise.”

Last week, the foreign secretary, Phillip Hammond, told parliament’s Intelligence and Security Committee he expected that minister who signed surveillance warrants would likely have to justify themselves in front of a public inquiry at some point in the future.

“I’m sure I can speak for all of my colleague who sign warrants that we all have, in the back of our minds, that at some point in the future we will – not might be, but will – be appearing before some inquiry or tribunal or court accounting for the decisions that we’ve made and essentially accounting for the way we’ve applied the proportionality and necessity tests,” he said.

Hammond was also criticised for some of his answers to the committee, with experts suggesting the foreign secretary appeared not to understand the legal framework for the warrants he was signing , following a mischaracterisation of which types of communication would or would not require individual warrants.

• This article was amended on 30 October 2014. An earlier version misnamed Mike Bochenek as Mike Bostock.