At the heart of the home affairs select committee's questioning of the Guardian editor Alan Rusbridger over the NSA leaks was an age-old dispute about the nature of press freedom.

The MPs were split between those who understood both the theory and practice of a free press and those who, even if they accepted the theory, could not stomach the practice.

But the latter group got nowhere in their pursuit of Rusbridger because he, in company with any decent freedom-loving journalist, had no problem in justifying his trade.

What was remarkable is that the whole thing happened at all. With the British press having obtained the right to its freedom from political control in the 17th century, here was parliament calling a newspaper to account for exercising that freedom.

Why, I kept asking myself, was an editor being required to explain himself to MPs? What makes them think they have the right to do so? Do they act for the people or against them?

Though Rusbridger was tactful enough not to spell out such objections, his nuanced replies to the impertinence of being asked about his intentions and actions was implicit.

I can be more explicit. Our business is disclosure. Our justification is informing the public. We are aware of the consequences of what we publish and take steps to avoid causing any possible harm. We do so within the context of the law.

So, given that Rusbridger is imbued with a press-freedom philosophy, he was able to bat away MPs' concerns without raising a sweat, despite bluster from a couple of them who sought to suggest he might be guilty of breaching the Terrorism Act.

Michael Ellis, the Tory member for Northampton North, launched into a quasi-courtroom cross-examination that prompted spontaneous laughter.

He was, however, a barrister without a proper brief. In accusing Rusbridger of communicating "top secret" material across frontiers, his main concerns were about the possible identification of gay people working at GCHQ and those – both gay and straight presumably – who took trips to Disneyland.

His Tory colleague, Mark Reckless, in less confrontational mode but heading down the same cul de sac, was more concerned about the fate of a FedEx parcel.

Neither, it should be said, bothered to use the words "public interest". Theirs was a narrow establishment interest, one that seems willing to grant the secret services unlimited powers without effective control. They were not interested in listening to rational justification and stuck fast to a single line of attack.

Rusbridger appeared just a little exasperated with the line of questioning after patiently explaining, time after time, that the Guardian had not identified anyone who was named within the 58,000 files obtained from the NSA whistleblower Edward Snowden. Names had been redacted in the pieces published by the paper. And the files sent to the New York Times had not been compromised.

But Rusbridger's central point, repeated at intervals, was how the publication of articles about the systems of mass surveillance in the US and UK had been greeted elsewhere – in most of Europe and the United States – with concerns about the need to provide better oversight of the activities of secret services.

While a necessary global debate about oversight was in progress, within Britain, the messenger was being blamed for the message. He said it was an attempt to intimidate the Guardian in order to prevent it from publishing stories of significant public interest.

He didn't need to say it. The fact that he was appearing before the committee proved his point.

Roy Greenslade is professor of journalism at City University, and was editor of the Daily Mirror from 1990-91