Matt Hancock
© Steve Parsons/PA
Very rarely do we come across a cache of documents giving an unvarnished glimpse of the personalities, as well as the policies, which shape our lives. Britain's 30-year rule shows us memos and scribbled comments, but with no hint of the conversations behind them. Richard Crossman's posthumous diaries were so explosive that ministers tried to suppress publication, but even that was just one man's view. Matt Hancock won't be thanked for it, but he has done the nation a great service by keeping perhaps the richest documentary source disclosed in recent years.

Conversations in and around 10 Downing Street would never normally be recorded. But Hancock's WhatsApp messages offer a real-time record of decision-making - complete with gossip, reactions, documents, conversations and emojis. They have several stories, to be sure, but the real value lies in something greater: a psychological profile of a group of men who had untrammelled power over the lives of millions. How would any group behave, in such circumstances? The Lockdown Files let us find out.

After reading thousands of these messages, the big theme is far more than the sum of the scandals. There's no end of those. At one stage we see that a convicted sex offender is suggested to bankroll a Matt Hancock leadership bid - which, it's explained, would be fine because he's a "lovely" chap who went to St Paul's and is "regarded fondly". There's plenty more chaos and skullduggery to be exposed in coming days. But the real value in The Lockdown Files lies in far more than the sum of the headlines.

We see how a group of men - given complete power and acting without scrutiny - move from being rational and cautious to dangerously gung-ho. They seem to revel in police being given "marching orders" to go after the general public. Even Simon Case, head of the Civil Service, says how much he'd like to "see the face" of first-class travellers incarcerated in "shoebox" hotels. So how did they get to this stage?

The WhatsApp messages show that things started by pointing out a "contradiction" in lockdown theory. It was not just a flaw, but the flaw: the models did not factor in just how much people watched the news and stayed home. A Treasury official lays it out: "If businesses are seeing revenues collapsing it suggests people are actually complying and not going into restaurants/shops/etc ... so how much additional benefit does 'locking down' actually get you?"

It wasn't just a hunch. Data were then shared with the WhatsApp group showing that 54 per cent of the public were socially distancing and 56 per cent no longer attending social gatherings. So Brits were being sensible, hunkering down. But this, it seems, was secret. "Just for us all to see," they were told. Still the WhatsApp group was behaving as it should: a genuine exchange of views, in a complex and fast-moving environment. Then, lockdown happened. Fast forward a few months and it was becoming embarrassingly hard to prove a link between lockdown and controlling the virus. Sweden was doing pretty well, in spite of having kept schools, pubs and restaurants open. Rather than ask what there was to learn, Hancock became enraged by what he called the "f-----g Sweden argument" and wanted it quashed. "Supply three or four bullet [points] of why Sweden is wrong," he asked of his aides. Not whether it was wrong: why it was wrong.

In coming days, this newspaper will show the treatment meted out not just to lockdown critics, but ministers asking awkward questions about what all of this would lead to. This shows the groupthink atmosphere: how hard it was, even as a Cabinet member, to urge caution. By the end, ministers were left in no doubt that anyone who asked questions would be seen by the No 10 team as a problem - or even the enemy. (Even, on occasion, the prime minister himself.)

It's a classic study of groupthink, but decades of study into so-called cognitive dissonance in political leadership shows we should expect this. The bigger the stakes, the stronger the denial. At a certain stage in a high-stakes drama, the politician starts to see their policies as not just correct but heroic and their critics as confused, malign or ideologically-motivated. A poor backdrop for error correction.

Public opinion also exerted a huge gravitational pull. The original pandemic plans imagined ministers being guided by science but did not envisage a situation where panic would see people demanding lockdown, as they saw happening in other countries, and resisting any relaxation of rules. The temptation to follow public opinion even led to the collapse of parliamentary opposition, as Sir Keir Starmer rubber-stamped every decision. Just a handful of voices were asking difficult questions or arguing for restraint: a small enough number to be easily dismissed as cranks.

There are signs of Boris Johnson growing alarmed at the lockdown machismo of his advisers. To Hancock's horror, he ended up taking advice from two academics, Raghib Ali and Carl Heneghan, who spotted that the graphs used to sell the second lockdown to the public were based on out-of-date data. "If this illustrates anything," Johnson says, "it is that red teams can work, but need to be formally established."

He was right. An effective "red team" was the missing element in Britain's pandemic response: a unit of experts to identify and flag up flaws in the government's argument. This was the only way of getting through what had become, by then, a powerful clique of pro-lockdown ministers and officials out to rubbish minority reports. If decisions are made in secret with the Cabinet left in the dark and the opposition having abandoned its post, there is no one to scrutinise. The whole democratic apparatus was suspended. So nothing to stop big mistakes from becoming bigger.

The problem with ignoring all lockdown questions until the official Covid Inquiry reports is that no lessons are learned and nothing will get fixed - leaving the country vulnerable to repeating the same mistakes. The new pandemic response needs to factor in not just the behavioural response of the public but of politicians - especially if they think no one is looking.

It was impossible to guess, before, just how they'd behave if they thought no one was looking. But thanks to The Lockdown Files, we certainly know now.