Not a good week, I grant you, to be holding up the US as a model of political conduct. It requires an effort of will to see past this month's shutdown fiasco and find something worthy of admiration.

And yet there it is. It's found in, of all things, the scandal of global mass surveillance undertaken by the US National Security Agency, in tandem with its British allies at GCHQ, and first revealed by the former NSA contractor Edward Snowden in the Guardian in June. War-on-terror hawks, and Homeland viewers, will doubtless admire the technical prowess of the NSA operations themselves. The latest revelations, published in the Washington Post, illustrate how the agency can locate the most wanted terrorists via their laptops: "The NSA is able to start downloading data in less time than it takes the targeted machine to boot up."

But that's not what I have in mind. No, what is worthy of praise is how the US political class has reacted to these disclosures. It puts to shame the response of Britain's own governing circles, in parliament and outside it.

In the US, no fewer than three separate bills are now before Congress, aimed at fixing the key problem that Snowden exposed – the ability of the NSA to operate beyond the reach of those lawmakers who were meant to scrutinise it. The notion of a government agency acting as a law unto itself has appalled members of the House and Senate, right and left alike. Leading the charge is no less a hawk than the author of the notorious Patriot Act, Republican Jim Sensenbrenner.

From the president downward, those at the very top of the US security establishment have conceded – while taking care not to give any credit to Snowden for starting it – that a debate about the NSA's activity, even one that throws a shaft or two of daylight on its work, was long needed.

The contrast with the reaction in the UK could not be sharper. The first response was one of denial. Not denial as in "that's untrue"; denial as in sticking fingers in your ears and going "la la la". In this the politicians were aided by the British press, much of which chose all but to ignore the story, even though the GCHQ element directly involves the UK. Some tried to suggest that Snowden had made no news, that he had simply disclosed that spies spy – as if it had been common knowledge that agencies in Maryland and Cheltenham were routinely keeping tabs on the calls, emails and online lives of every last one of us.

Indeed, for many British newspapers the first engagement in this affair came when the head of MI5, Andrew Parker, condemned the leaking of the NSA files. Previously mute on this intrusion into the private lives of ordinary British citizens – having been laudably vigilant on, for example, the "snooper's charter", in the past – the Daily Mail suddenly found its voice, attacking the Guardian for publishing Snowden's revelations and acting with a "lethal irresponsibility" that could only aid the terrorists.

That led to the second response, echoed this week in Westminster: shoot, or at least jail, the messenger. Liam Fox, who as a Tory rightwinger might be expected to be a staunch defender of personal freedom, called instead for "an assessment" of whether the Guardian had damaged national security. Others mutter darkly about prosecutions under the Official Secrets Act. Quick to react, Keith Vaz's home affairs select committee will now do as Fox demanded – and investigate the behaviour of the Guardian (rather than, say, GCHQ).

This should embarrass all those who like to bang on about Westminster as the mother of parliaments, citing the Magna Carta and praising the Commons as the custodian of our liberties. What guff. In our system, parliament is meant to be sovereign. Yet here, in GCHQ, is a state agency operating apparently beyond the reach of parliament, extending its remit without the permission or even the knowledge of MPs. Of all the revelations of the last few months, among the most shocking was Chris Huhne's admission that he had had no idea what GCHQ was up to – even though he was a cabinet minister with a seat on the national security council. MPs need to put aside the issue of the Guardian, which merely switched on a light in a darkened room, and realise that all this is an affront to parliament.

Perhaps they don't care much about privacy. Maybe they don't mind who collects and reads their, or your, emails. Many might accept the old cliche that if you have nothing to hide, you have nothing to fear. Despite all that, they should still be outraged. For they are the legislature, charged with scrutinising the executive – and yet here is an arm of the executive that is deemed off limits to them, that can do what it likes regardless of the law.

Some MPs will answer that all is in hand now Malcolm Rifkind's intelligence and security committee has announced it will investigate the matter. That's a welcome development, but MPs need to keep that committee's feet to the fire – ensuring it defies its reputation as a creature of the executive (its nine members must first be nominated by the prime minister before they can be approved by parliament); one that is easily rolled by the security services. Those nine members need to ask what the agencies have been doing and, assuming their committee did not know about it, why the hell they were kept in the dark.

And while we're at it, where is the opposition? Ed Miliband's Labour leadership was born in part by a desire to break from the Iraq-war era deference to the US security machine. Now we have concrete evidence that GCHQ acts in direct, daily collusion with the NSA, even if that means trampling on the privacy of tens of millions of British citizens. To be sure, Miliband has to pick his battles. But if he is to be consistent he cannot duck this one.

Now Facebook, Microsoft, Google, Yahoo and Twitter are calling on parliament to act, aware that customers will soon lose confidence in their services if they believe that Big Brother is always looking over their shoulder. In other words, the US Congress, the tech giants, even the US intelligence apparatus itself have all understood before Westminster that the time has come for a serious debate about internet surveillance, what is permitted and who should oversee it. If Britain's parliament is to live up to its own grand rhetoric as the defender of liberty and seat of sovereign power, it needs to catch up fast.

Twitter: @Freedland