The first revelation from the Snowden documents, less than two years ago, exposed systematic storage and analysis of all Americans’ telephone records by the National Security Agency and the FBI. As of midnight last night, that programme – launched in secrecy soon after 9/11 by the then vice-president, Dick Cheney – is over. Congress refused to sanction the continuation of domestic mass surveillance in the guise of collecting “business records”. The clear mood was that substantial restrictions on NSA surveillance had become inevitable.

Outside the US, some proponents of surveillance have travelled in the opposite direction. France passed an intrusive new internet surveillance law less than a month ago. Australia has done the same. Emboldened by the election victory and no longer restrained by principled Lib Dem concerns, Theresa May now pledges to force her souped-up investigatory powers bill on the UK.

I was asked to start the conference discussions, sitting beside GCHQ’s new director, Robert Hannigan

But despite the machismo of political discourse, and what intelligence chiefs have publicly professed about “capability gaps”, it appears that in private many lessons from Snowden have been understood.

Two weeks ago at Ditchley Park, a thinktank and conference centre near Oxford, a remarkable follow-up to the revelations took place when Sir John Scarlett, the former chief of SIS – the Secret Intelligence Service, or MI6 – presided as 40-plus participants from around the world spent three days intensively reviewing changed approaches to intelligence, security and privacy.

I was asked to start the conference discussions, sitting beside GCHQ’s new director, Robert Hannigan. In attendance was a veritable band of Big Brothers – current and former CIA, GCHQ and SIS chiefs, current and former European spy bosses, counter-terrorism commanders. From the private sector, there were Google, Apple and Vodafone policy staff, alongside European legal experts. Although Hannigan attended only the first discussion, another senior GCHQ director stayed to the second day.

Discussions followed the Chatham House rule, freeing officials to offer personal opinions, with other participants undertaking not to say who said what. Following Hannigan, I emphasised transparency, accountability, disclosure (including post hoc disclosure to surveillance subjects), and legal sanctions for breaches as means to deal properly with competing human rights.

Snowden – love him or hate him – had changed the landscape towards transparency, or at least 'translucency'

No one present argued against calls for greater openness. That’s a first: coming 40 years after a time when it was in effect a crime in Britain even to mention the existence of GCHQ, and programmes on the subject were banned. Nor was trust a given. “There must be oversight – do not assume agencies will follow the rules,” one discussion concluded.

Perhaps to many participants’ surprise, there was general agreement across broad divides of opinion that Snowden – love him or hate him – had changed the landscape; and that change towards transparency, or at least “translucency”, and providing more information about intelligence activities affecting privacy, was both overdue and necessary.

“We should have seen it coming in the first place, and put more information in the public domain first,” was another observation.

I did not hear the phrase “capability gap” mentioned. That sort of rhetoric seemed to be reserved for the political arena. Away from the populist headlines, I heard some unexpected comments from senior intelligence voices, including that “cold winds of transparency” were here to stay. An event like this would have been inconceivable without Snowden.

One of the stipulations made by the intelligence officials and regulators alike was that there should be “no secret laws” unavailable to the public. Sir David Omand, the former GCHQ director and Home Office permanent secretary, has written that “investigative activity should be regulated by ‘black letter law’”. Another suggestion made by Omand (who attended the Ditchley conference) that “not everything that technically can be done should be done” was not disputed at the event.

Other points of agreement were that agencies needed strong external controls, including supervision of internal ethical controls. Oversight should not govern just what was collected, but needed to expand to include the “combination of data” (such as massive metadata analysis), “information sharing”, and the “use of intelligence collected”. Internet companies should not have to face “ad hoc approaches and conflicts of law”. Agencies were asked to use the front door in making requests for law enforcement data, and not (as hitherto) steal it from internal networks by hacking or by intercepting data flows.

A different senior speaker reflected that Snowden’s actions were an inevitable, and perhaps necessary, counterbalance to excesses of intelligence collection after 9/11, while also considering his disclosures “hugely damaging”. You don’t get nuanced thoughts like that in most British newspapers these days.

The fact of GCHQ’s director and other serving intelligence chiefs attending the conference may also have been a quiet signal, perhaps speaking to an awareness that their employees could be more sensitive than leather-skinned political bosses to public concerns. That would be another reason to bring on more transparency.