GCHQ has just confirmed this practice:
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.
Of course, whether its a "deliberate circumvention" is up to GCHQ and decided in secret, and its a fair bet that they never refuse to take information on this basis.
UK Ministers have gone on record to state that a warrant is required for all interception and analysis of UK data. GCHQ has just shown that they lied. We can't trust our spies, and we can't trust what our politicians tell us about them. The only way to be safe from mass-surveillance is to shut them down, permanently.