Wednesday’s debate in parliament’s Westminster Hall on oversight of Britain’s intelligence services was meant as a rebuttal to that initiated last week by Conservative MP Julian Smith on whether the Guardian had endangered national security by publishing surveillance leaks from Edward Snowden.

Instead the debate sponsored by three MPs underscored the degree to which all three main parties are intent on suppressing evidence of mass surveillance by the US National Security Agency and the UK’s Government Communications Headquarters (GCHQ). The debate—called by Julian Huppert of the Liberal Democrats, Conservative Dominic Raab, and the Labour Party’s Tom Watson—renewed threats against the Guardian and Snowden.

The three-hour debate proceeded in the shadow of Monday’s threat by Prime Minister David Cameron, made in parliament proper against the Guardian and other newspapers. Cameron warned the media to show “social responsibility” when reporting leaks from the NSA and GCHQ, or they would face high court injunctions and/or the use of D Notices to prevent the publication of information that could damage national security.

A D notice, more properly a DA or Defence Advisory Notice, is a request from government to newspapers to keep silent on any issue the government sees fit to identify as sensitive. Cameron said his preference was to talk to newspapers rather than resorting to legal action, but he was faced with the danger of a “lah-di-dah, airy-fairy view” of the dangers of leaks.

“I don’t want to have to use injunctions or D Notices or the other tougher measures. I think it’s much better to appeal to newspapers’ sense of social responsibility. But if they don’t demonstrate some social responsibility it would be very difficult for government to stand back and not to act,” he said.

Cameron’s comments were cued for him by Conservative Party MP Julian Smith, the government’s foremost attack dog against those who dare challenge the NSA and GCHQ’s mass surveillance.

In Westminster Hall, Huppert opened by stressing that democratic legitimacy demands supervision of the services is set on a firm legal basis. He professed his admiration of “the security services; the work that they do is fundamental to our fight against crime and terrorism, not only in the UK but beyond our borders.”

Hupert noted that the US and UK are devoting vast resources to break encryption systems and asked what the reaction would be if China were to do the same. With even the National Security Council reportedly unaware of the operation of Britain’s Tempora surveillance programme and the US’s Prism it is hard for parliament to scrutinise legislation, he said, adding that the UK also needs independent scrutiny of the Regulation of Investigatory Powers Act and the Intelligence Services Act.

Huppert met with repeated hostile interventions, beginning with Julian Smith who asserted that security officials have been put at threat by the Guardian’s reporting.

Labour’s Hazel Blears joined in, asking Huppert if he accepted “that virtually every operation that has foiled a terrorist plot in this country has been dependent on communications data over the past decade or so, and that it is essential for our agencies to have those powers, but obviously within a robust legal framework?”

Tom Watson noted that Tempora “has been mining our internet communications data without public knowledge on a colossal scale [and] we only know of the existence of the Tempora programme because of the actions of Edward Snowden and the Guardian newspaper.” If the law “permits such fundamental abuse of liberty, the law is wrong and must be changed,” he said.

Dominic Raab again began with a pledge of appreciation for the security services, before stating, “The legal basis for Operation Tempora looks thin at best, and Parliament certainly had no idea of the scale of the use of those powers. We also learned that Britain receives data from the US Prism surveillance programme, which appears to allow GCHQ to dilute—not circumvent entirely, but dilute—the safeguards that would apply if the same agencies were to gather the information themselves.”

In the debate that followed, Labour’s David Winnick spoke in defence of the Guardian. “What the Prime Minister said on Monday is very much a threat to the press,” he said.

He was attacked by Tory Adam Holloway, who demanded to know, “If in the last few weeks, we had lost a city to nuclear terrorism or there had been a gigantic mass casualty, I wonder whether the hon. Gentleman’s constituents would see Edward Snowden as a trendy, cool whistleblower or as a traitor.”

Julian Smith used this as an occasion to again accuse the Guardian of endangering national security. For invoking this canard he was praised by Labour’s George Howarth for his “measured, thoughtful speech.” The Guardian was “probably” entitled to publish Snowden’s leaks, but not “wise” to do so, Howarth said.

Howarth, a member of the Intelligence and Security Committee, made an extended defence of the NSA’s Prism programme. The Intelligence and Security Committee (ISC) had looked at it and issued an interim statement in July that found GCHQ did not circumvent UK law by using it.

Watson then asked, prompting laughter from Huppert, whether it was only after the Guardian’s revelations that the ISC had examined the issue. “It was after the Guardian revelations. The hon. Member for Cambridge seems to think that that is funny,” Howarth replied.

Blears stepped in again to defend the ISC, stressing, “It is an essential part of the debate that the agencies were operating within the existing legal framework of British law.”

Tory Ben Wallace cynically asserted, “Let us be clear that spies spy.” The Guardian “has yet to specify any crime committed by the British Government, authorities or spies.” Wallace implied the newspaper could face prosecution, and menaced Snowden. “I am not sure whether he is a traitor, but I question his judgment about the countries to which he decided to run off.”

Labour’s John McDonnell welcomed “what the Guardian has done” as “heroic” and advanced a series of “practical” proposals to strengthen oversight. He criticised the ISC, as did Labour’s Michael Meacher.

This prompted Liberal Democrat Martin Horwood to rally to the intelligence apparatus’ defence. “We cannot make it childishly simple for those who would do us harm to evade surveillance,” he said.

Tory Sir Malcolm Rifkind, who heads the ISC, defended its record. When asked by Meacher to explain “why the Committee did not find out about the Tempora programme when it began to operate,” as indicated by Howarth, he responded, “The right hon. Gentleman does not have the faintest idea whether the Committee was aware of programmes of any kind. We are given classified information…”

Replying for the government, Home Office minister James Brokenshire baldly insisted that oversight of the secret services must itself be secret.

With apparently unintended irony, he added, “It is also important to highlight that, at a political level, the intelligence agencies are ultimately accountable to the Prime Minister, but on a day-to-day basis it is Secretaries of State—primarily my right hon. Friends the Home Secretary [Theresa May] and Foreign Secretary [William Hague]—who are responsible for balancing the need to protect national security and the need to fulfill their duty to protect the British public against the potential intrusion on individuals’ rights to privacy that could be caused by intelligence activity.”