A committee of MPs challenged the existing system of oversight for the security services by asking the head of MI5 to justify his claims that the Guardian has endangered national security by publishing leaks from the former NSA contractor Edward Snowden.

In an unprecedented step, Keith Vaz, the chairman of the home affairs select committee, announced that spy chief Andrew Parker had been summoned to give evidence in public to the Commons committee next week.

The decision was taken at a private session of the select committee on Tuesday before the body heard evidence from Guardian editor Alan Rusbridger seeking to justify the Guardian's decision to publish a string of stories based on US and UK intelligence agency files leaked by Snowden to the media.

Although last month the security services appeared in public for the first time to give evidence to parliament, they appeared before the Intelligence and Security Committee (ISC). Members of that committee are appointed by the prime minister and tend to have defence or a security background. Commons select committees, by contrast, are parliamentary committees, with the chairs and members elected by MPs.

It is understood that the home affairs select committee rejected inviting Parker to give evidence in private. Julian Huppert, a Lib Dem member of the committee, said: "A precedent has been set and now that the heads of the security services have given evidence once in public they should do so again to us, and not just to MPs they would like to have ask them questions. I would expect Mr Parker to attend."

Labour committee member David Winnick also pointedly ridiculed the ISC referring to the way in which Britain's three main spy chiefs had been given prior notice of the questions in its first public evidence session last month. Some committee members want Parker to reveal how much MI6 and MI5 had told the ISC about its mass programme of surveillance, so in effect testing the value of the ISC as a constitutional check on the security services. Deep political divisions over the Guardian's publication of the Snowden files were exposed throughout the one-hour cross examination of the Guardian's editor, with Tory MPs rigidly focusing on whether the newspaper had broken the Terrorism Act by sending the names of UK agents abroad as documents were shared with the New York Times.

Cressida Dick, the Met's Assistant Commissioner who heads London's Specialist Operations unit, told the committee in subsequent testimony confirmed that the Metropolitan police was looking to see whether individuals had broken Section 58A of the Terrorism Act, saying she would go wherever the evidence took her. "It appears possible ... that some people may have committed offences," she said, but declined to specify whether the Guardian is under investigation.

Following the session Julian Smith, the Conservative at the helm of Tory criticism of the Guardian, went so far to accuse Rusbridger of treason. The MP said that Rusbridger had "admitted the names of British agents were in documents he could not bother to read, but he sent abroad to America. The Terrorism Act 2000 makes it an offence to communicate the names of the agents that protect us. It is for the police to take the decisions, but I hope he is prosecuted."

Rusbridger told the committee he did not know if the police were conducting an inquiry, but promised the paper would not be intimidated from publishing stories that it regarded were in the public interest. He said approximately 1% of the 58,000 intelligence files leaked by US whistleblower Snowden have been published by the paper. He had consulted government officials prior to the publication of every story, but one. He explained the files had originally been placed in four locations – with the Guardian, the Washington Post, a location in Rio de Janeiro and a location in Germany. "That's the hand of cards we were all dealt – The Guardian, security services and governments." Vaz referred to Parker's claim that the Guardian had gifted the terrorists the ability to attack at will, saying "this is severe criticisms of a kind I have not seen before from the head of our security services".

Rusbridger countered that "the problem with the accusations is they tend to be very vague and not rooted in specific stories" adding the publication of the NSA files "leaps over the hurdle of public interest". He said: "There is no doubt in my mind ... that newspapers have done something that oversight has failed to do".

He pointed to a series of senior UK and US officials that had described the Guardian's behaviour as incredibly responsible, insisting the Guardian was not a rogue newspaper, but acting in concert with other responsible newspapers to publish stories .

In possibly the most heated exchanges Conservative MP Michael Ellis insisted he would not be a party to "a Labour love-in", and asked Rusbridger, "if you'd known about the Enigma code during World War Two would you have transmitted that information to the Nazis?"

Ellis suggested to Rusbridger by using Fed-Ex to communicate some of the NSA files, containing the names of intelligence officers, he had committed a criminal offence. "It isn't only about what you've published, it's about what you've communicated. That is what amounts, or can amount, to a criminal offence," Ellis asserted.

"You may be a lawyer, Mr Ellis, I'm not, so I will leave that with you," the editor replied. He also pointed out "We have never used a single name. We have published no names and we have not lost control of any names". The files sent to the US were encrypted to military grade and had not been compromised, he said.

Ellis also clamed the Guardian may have exposed the identity of gay GCHQ staff, or GCHQ families that had been on a trip to Disneyland in Paris. Rusbridger pointed out the fact that there was a Pride branch of GCHQ was on the website of Stonewall, the gay rights pressure group.

At one point Vaz took an unexpected tack, asking the editor whether he "loved this country." A startled Rusbridger replied: "We are patriots and one of the things we are patriotic about is the nature of our democracy and of a free press. There are countries and they are not generally democracies where the press are not free to write about this and where the security services do tell editors what to write. That's not the country we live in, in Britain, and it's one of the things we love about the country."