David Cameron has endorsed a speech by Andrew Parker in which the new head of MI5 suggested that the leaks by the US whistleblower Edward Snowden had undermined the fight against terrorism.

The No 10 spokesman said: "The prime minister thinks it was an excellent speech and we are, as you would expect, always keeping under review the measures that are needed to contribute to keeping our country safe."

Parker did not mention Snowden by name in a speech that defended Britain's intelligence agencies. But his remarks appeared to be aimed at the whistleblower who gave thousands of intelligence files to the Guardian that revealed surveillance programmes carried out by GCHQ and its US counterpart, the National Security Agency (NSA).

Alan Rusbridger, the editor-in-chief of the Guardian, defended the newspaper's reporting of files leaked by Snowden that highlighted formidable technologies "beyond what Orwell could have imagined".

Rusbridger told The World at One on BBC Radio 4: "If you read the whole of Andrew Parker's speech it is a perfectly reasonable speech and it is what you would expect him to say. If you are on the security side of the argument you want to keep everything secret, you don't want a debate and you don't want the press or anyone else writing about it. But MI5 cannot be the only voice in this debate."

Rusbridger challenged Parker's claim that the leaking and publication of the NSA files posed a risk to national security. He said: "Glenn Greenwald [the Guardian journalist who received the leaked documents] has a phrase that you would have to be a terrorist who didn't know how to tie his shoelace not to believe that people were watching things on the internet and scooping up telephone calls. I don't think some of this will come as a great surprise to terrorists.

"But what is significantly new about what we have been revealing is the extent to which entire populations are now being potentially put under surveillance. I have just spent a week in America where everybody is talking about this from the president down."

Rusbridger warned of attempts in the US to prevent reporting. "There has to be a balance. There have been instances in the last few months where people have gone through metadata to find out reporters' sources … These technologies are formidable. They are beyond what Orwell could have imagined.

"It may be that everything in a social democracy is fine and the oversight is working. But I would be very surprised if the current oversight methods really understood and knew about some of the things we have been describing as a result of the Snowden revelations."

In his speech the MI5 head defended the work of GCHQ and warned of the dangers of publishing documents which reveal some of its systems. Parker said: "We are facing an international threat and GCHQ provides many of the intelligence leads upon which we rely. It causes enormous damage to make public the reach and limits of GCHQ techniques. Such information hands the advantage to the terrorists.

"It is the gift they need to evade us and strike at will. Unfashionable as it might seem, that is why we must keep secrets secret, and why not doing so causes such harm."

Asked whether Cameron agreed with Parker that the leak of the Snowden files had been a gift to potential terrorists, the No 10 spokesman said: "I would happily point you to all parts of the director general's speech. It was an excellent speech."

Asked whether the prime minister's endorsement covered Parker's claim that making public GCHQ's techniques provided "the gift they [terrorists] need to evade us", the spokesman said: "Including that".

The spokesman's remarks suggest Cameron agrees with MI5 that the government should try and revive the data communications bill, which has been dubbed the snooper's charter. The proposed legislation was blocked by Nick Clegg.

Asked whether Parker's remarks showed that the bill was not dead, the spokesman said: "The position hasn't changed. The government continues to consider how best we continue to ensure our intelligence agencies, our law enforcement agencies are able to stay up to date in what is – in one of the points Andrew Parker was making – a continually evolving technological environment."

A Guardian News and Media spokeswoman said: "A huge number of people - from President Obama to the US director of national intelligence, James Clapper - have now conceded that the Snowden revelations have prompted a debate which was both necessary and overdue.

"The president has even set up a review panel and there have been vigorous discussions in the US Congress and throughout Europe. Such a debate is only worthwhile if it is informed. That is what journalism should do."