It has been almost a year since Edward Snowden electrified the debate about surveillance by leaking documents that set out some of the capabilities used by British and American intelligence agencies.

The response to this in Westminster has been punctuated by periods of indifference, heavy-handedness and blind fury, but in recent months the political classes have stopped arguing about whether Snowden is a criminal or a traitor and begun to consider whether he might have had a point. Today, the home affairs select committee concludes emphatically that he does.

The committee's report might become an important landmark if Labour and the Liberal Democrats stand by their pledges to fundamentally review the scrutiny of MI5, MI6 and GCHQ during the next parliament.

That is what the document calls for, and the committee chair, Keith Vaz, even suggests the media felt "compelled" to continue publishing stories because it was the only way to get MPs to sit up and listen.

When his cross-party committee did this, they reached some stark and unforgiving conclusions.

Broad assertions that "current oversight is not fit for purpose", and that the principle law governing spying activity needs to be reviewed, are supplemented by digs at the high-handed attitude of the agency chiefs, as well as the body that oversees them, the Intelligence and Security Committee (ISC).

In what amounts to a drive-by shooting, no part of the existing oversight regime is spared denunciation, either.

The ISC has been misled before, particularly over Iraq, and needs to be reformed, the report says.

The part-time commissioners who provide scrutiny of the agencies are not doing enough spadework, and their remits are mired in confusion.

The Regulation of Investigatory Powers Act (Ripa), which codifies what the agencies can do, is branded a law from a different age and needs to be refreshed.

These criticisms will irritate Tory cabinet ministers, who have refused to engage with the surveillance debate over the last 11 months – and they regard Vaz as a nuisance.It will also irritate the former Tory cabinet minister Sir Malcolm Rifkind, the current chair of the ISC, who has launched his own inquiry into the questions raised by Snowden's revelations.

By coincidence, this investigation began in earnest this week, with the first oral, behind-closed-doors questioning of intelligence chiefs.

But while the ISC will seek to rise above the criticism, Rifkind will know that any report that falls short of today's analysis could be branded a whitewash and provide more ammunition for critics who have argued the ISC is too close to the people it has been tasked to keep control of. That might be unfair, but the landscape of the debate has changed significantly over the last three months.

Downing Street might have been slow to realise this, but the agencies have not.

Their mood towards Snowden will never change – there is bitterness at the way their secrets have been paraded in public, and concern about how to recover capabilities that might have been compromised. But there also seems to be an acceptance that they need to do more to explain.

Senior voices in the intelligence community concede that if scrutiny of the agencies is not credible, then their claims of abiding by the law will always ring hollow.

Snowden will always be a divisive figure; there might never be a consensus over what he did. But on one matter there is growing political agreement. The old ways of scrutinising the intelligence agencies aren't persuasive anymore. They need to change.