Britain's spy agencies may be operating outside the law in the mass internet surveillance programmes uncovered by the US whistleblower Edward Snowden, according to Lord Blencathra, the former Conservative Home Office minister who led a formal inquiry into the data communications bill.

The Tory peer – David Maclean when he was an MP – said he felt "deeply, deeply uneasy" about programmes that allow the security services to examine the internet activities of British citizens without the consent of parliament.

In an interview with the Guardian, Blencathra said that the public had a right to know their internet data might be "lifted" and shared with US intelligence services – and that MPs should either vote to approve the surveillance programmes or put a stop to them.

He also condemned the fact that his committee scrutinising the data communications bill – subsequently killed off by the Liberal Democrats – was never told about GCHQ's existing mass surveillance capabilities. A joint memo from MI5, MI6 and GCHQ made no mention of them, he added.

"Some people were very economical with the actuality. I think we would have regarded this as highly, highly relevant. I personally am annoyed we were not given this information," said Blencathra, who was an ally of Michael Howard and considered on the right of his party .

Before the draft data communications bill was shelved, Blencathra's committee said it was very concerned that its proposed surveillance powers were far too wide-ranging and recommended changes to limit its scope.

Blencathra's intervention came hours after sharp criticism of the intelligence agencies by another peer, the former director of public prosecutions Lord Macdonald, who condemned the way the new head of MI5 had dismissed calls for greater scrutiny. Last week Andrew Parker said this would affect the way MI5, GCHQ and MI6 did their work.

Macdonald, who is now a defence lawyer, said Parker was employing "foolish, self-serving rhetoric". An urgent review of the intelligence laws and oversight was essential to stop "an increasing subservience of democracy to the unaccountability of security power," he added. "The law should be the master of technology. Anything else risks a spiralling out of control."

Blencathra is one of the most senior Conservatives to express reservations about the Tempora programme, which allows GCHQ to harvest, store and analyse millions of phone calls, emails and search engine queries. The agency does this by tapping the transatlantic cables that carry internet traffic, and shares the data with its American counterpart, the National Security Agency.

While Blencathra said he did not like unauthorised leaks, he admitted feeling sympathy for Snowden because of the importance of what he had disclosed. "We dislike leaks. Yes, we disapprove in many ways of what the Guardian has done, but at the same time we are deeply, deeply uneasy about what has been going on.

"I do not want people like Mr Snowden endangering national security. But I do not want our national security apparatus operating in what seems to me to be outside the law or on the very edge of the law. Or if it is just within the law, certainly without parliament knowing. Many of us are happy to have certain information collected by the state but, by God, we've a right to know the parameters under which they are operating."

He added: "Doing a deal with American security services to share information they have lifted about Brits I think is something the British public, through parliament, should either stop or consent to."

Blencathra said the existence of Tempora and an NSA programme called Prism was "highly, highly relevant" to his committee's inquiry into legislation that would have given further surveillance powers to the authorities.

Ministers argued the communications data bill, known by its critics as the snoopers' charter, was necessary to catch terrorists, but it was scrapped by the coalition over privacy fears. Snowden's leaks suggest the security services already have access to much of this information.

"The committee was not made aware at all of anything relating to Prism or Tempora, or even given any hint. We had a joint memo from MI5, MI6, GCHQ setting out why in their view the bill was essential, the usual stuff you get on terrorists, paedophiles, organised crime. But there was no hint whatsoever they were engaged in [these] programmes.

"I certainly feel we were given less information than the committee should have had. I am not suggesting we were deceived or misled but someone or some people were very economical with the actuality. I think we would have regarded this as highly, highly relevant. I personally am annoyed we were not given this information."

Blencathra said Snowden had revealed information that people "have a right to know about".

"A lot of people went into overdrive saying Snowden's a ghastly traitor, he's endangered national security. That may be true. But he's revealed things government were doing which the governments maybe ought not have been doing or we had a right to know about. Snowden is the first leaker I have ever felt sympathy for or felt had a potential justice behind what he was doing."

Blencathra dismissed the view of Sir David Omand, the former head of GCHQ, who said the leaks were the most "catastrophic loss to British intelligence ever".

He said this claim was "utter rubbish" and that comparisons with the leakers of secrets in the cold war era were exaggerated: "The Cambridge spies were revealing information that could have brought down the whole British government, the western world, nuclear secrets, the whole shooting match. To try and paint Snowden into the same box as Philby, Burgess, Maclean, Blunt is just outrageous."

His remarks chimed with those of Macdonald, who described Britain's intelligence laws as "anti-modern", and said Snowden's revelations had shown the "sickly character of parliamentary oversight of the security agencies".

Macdonald said the present chair of the intelligence and security committee, the former foreign secretary Sir Malcolm Rifkind, was "badly compromised" and appeared to be too close to the organisations he was supposed to be holding to account.

With a growing number of senior figures in Whitehall now calling for greater scrutiny of the agencies, Nick Clegg will this week begin to assess what might be done to give more muscle to the oversight regime. Clegg indicated last week that there was a "total legitimate debate" to be had regarding the new technologies deployed by GCHQ and other intelligence agencies, while David Cameron has voiced full support for the head of MI5's position.