Former Foreign Office lawyer says claim that reporting on reach of GCHQ and NSA breaches national security is ‘difficult to take’

A Conservative MP and former Foreign Office lawyer has criticised the MI5 director general, Andrew Parker, for suggesting that the Guardian's reporting of the NSA files was a "gift" to terrorists.

Dominic Raab said that the files leaked by whistleblower Edward Snowden had highlighted the "reach" of British and American intelligence agencies and had not disclosed interception techniques or sources.

Speaking in a parliamentary debate on surveillance at Westminster Hall on Thursday, Raab also asked why nobody from the Guardian had been charged or arrested after Theresa May suggested that lives have been put at risk by the disclosure.

"Either UK law enforcement is surprisingly slow, given these assertions that have been made, or national security is being used as a fig leaf to muzzle disclosures," he told MPs.

But a Conservative MP who recently wrote to the Metropolitan police to call for a criminal investigation into the Guardian accused the newspaper of potential treason. Julian Smith told MPs: "The Guardian, which had every right to report on this issue, which has raised important topics of debate, which has done so in a digital and global way and an interesting way – with good journalism – has threatened the security of our country and which today stands guilty potentially of treasonous behaviour."

Raab opened his speech by praising the work of MI5 and GCHQ, with whom he worked as a Foreign Office lawyer. But he took issue with Parker's claim that the disclosures about the work of GCHQ in the NSA files had helped terrorists.

Raab said: "In his speech the MI5 director general lambasted the Guardian for handing terrorists a gift – a very potent word he used. Ministers have more recently claimed that the disclosures have put lives at risk.

"I want to take that seriously because Mr Parker claimed that making public 'the reach and limits of GCHQ breaches national security'. Let us be very clear about what was being talked of here – not disclosing interception techniques, not the technical aspect, not the revelation of source or operatives – clearly a major cause of concern if that were to happen. Simply revealing our intelligence reach. I find this assertion difficult to take at face value. It may be true but it is not on the mere assertion."

Raab questioned whether national security had been breached because terrorists knew their communications were being routinely monitored. He said: "Any serious terrorist group assumes their phones, emails and internet use will be monitored. That is no secret. Learning that western spies drain the swamp of their own citizens' data in the process does not help terrorists in any tangible way.

"If national security were materially breached why hasn't anyone at the Guardian been charged or even arrested since the search of their offices back in July? Why wasn't David Miranda, detained for several hours, arrested and then bailed following his detention at Heathrow in August?"

Meanwhile, Smith accused the Guardian of having failed to discuss the documents with the government even though its editor-in-chief, Alan Rusbridger, held a meeting with the cabinet secretary, Sir Jeremy Heywood. This led the Guardian to agree to destroy hard drives after Heywood threatened to block further publication of details of the files using a high court injunction.

Liberal Democrat MP Julian Huppert challenged Smith, saying: "Is he aware that [they] been in touch for many, many months to talk about these things? Does he think part of the onus should be on the government to provide advice if it is concerned about these things?

"The Guardian is quite happy to talk about how to make sure this [data] is secure and frankly the NSA should never have lost it in the first place."