For decades, ministers and officials have come up with the pat response, ‘We can neither confirm, nor deny’, when asked about operations by MI5, MI6 and GCHQ.

This week, the policy of NCND, as it called in Whitehall, will come under unprecedented pressure in the wake of Edward Snowden’s revelations, as individuals and organisations ask whether they have been targeted by Britain’s security and intelligence agencies. NCND will be tested as never before as the country’s most secretive court hears complaints – mostly in public – that GCHQ’s mass surveillance of the internet violates human rights.

The case against the government’s electronic eavesdropping agency is being heard by the investigatory powers tribunal (IPT). It has been brought by Privacy International, Liberty, Amnesty International, the American Civil Liberties Union and a number of other human rights groups.

“NCND”, cry government officials as they are asked about the increasingly intrusive activities of its intelligence agencies. The government’s sole response when asked about Snowden’s disclosures is that whatever our spooks do is permitted under the law. The trouble is the law contains many loopholes.

NCND has meant that the investigatory powers tribunal has declined to say whether complainants have ever been targeted by spies, whether lawfully or not. It is as though its title was conjured up in Whitehall as a deliberate irony: a curtain the spooks, with the tribunal’s ready connivance, have hid behind. That curtain is becoming increasingly threadbare. Just how threadbare is demonstrated by a 48-page defence of the spooks presented to the tribunal by the leading Home Office counter-terrorism official, Charles Farr.

He prefixes his long justification of the activities of the security and intelligence agencies, GCHQ in particular, by judicious use of such words as “if’”, and “alleges”.

Farr, the director general of the office of security and counter-terrorism in the Home Office, says that searches on Google, Facebook, Twitter and YouTube, as well as emails to or from non-British citizens abroad, can be monitored by the security services because they are deemed to be “external communications”. It is the first time that the government has admitted that UK citizens, talking via supposedly private channels in social media, are deemed by the British government to be legitimate legal targets that do not require a warrant before interception.

Farr admits the existence of Prism – an NSA interception programme – on the grounds it had been “expressly avowed by the executive branch of the US government”. He says he can admit that GCHQ obtains information from Prism because the parliamentary intelligence and security committee has said so. “However,” adds Farr, “beyond this confirmation, I maintain … the ordinary ‘neither confirm nor deny’ stance on intelligence matters.”

Thus, he explains, he cannot say whether or not GCHQ passes on Prism intercepts to the domestic security service, MI5, or the foreign intelligence-gathering agency, MI6.

He also says he cannot comment on whether GCHQ, with the NSA, taps into the network of fibre-optic cables which carry international phone calls and online traffic in the monitoring programme, code-named Tempora. The project, disclosed by Snowden, has been described by its designer as “mastering the internet”, enabling GCHQ and the NSA to process huge quantities of communications between innocent people, as well as targeted suspects. As many as 600m “telephone events” a day can be recorded.

Farr says he can “neither confirm nor deny” the existence of the now much-publicised Tempora programme. He refers to an “alleged Tempora interception operation”. He adds: “All I am able to confirm is if [he underlines] the Tempora operation existed” it would have been carried out legally.

Farr goes on to say the government had admitted that David Miranda, partner of former Guardian journalist Glenn Greenwald, was in possession of some 58,000 “stolen classified GCHQ documents” when he was arrested under the Terrorism Act 2000 last year. But he says the government had not admitted that the documents formed the basis of media articles about Tempora. Nor had the government confirmed or denied “the provenance of any particular document that is alleged to have been stolen by Mr Snowden”.

NCND has become a farce. GCHQ does carry out the kind of activities the Guardian and others have written about on the basis of official documents revealed by Snowden, a former NSA contractor. Otherwise, there would be no point in Farr going on about them, albeit in such an elaborately coy manner.