One disk, six reporters: The story behind the expenses story

On a normal Wednesday while parliament is sitting, Robert Winnett can be found squeezed into the Commons press gallery watching Prime Minister's Questions. But on 29 April, The Daily Telegraph's deputy political editor was mysteriously absent.

The quiet, young, former personal finance reporter, known affectionately by colleagues as "rat boy" for his scoop-sniffing cunning, had locked himself in a back room at the Telegraph offices a mile down the road over Victoria Station. In a training room tucked off a dead-end corridor that would soon be nicknamed "the bunker," he and a carefully picked team of colleagues spent nine days secretly wading through a hard drive containing four million items of data that had been smuggled out of the Commons expenses office and sold to the Telegraph for a six-figure sum.

The immensity of the task in converting what one close to the operation describes as "the equivalent of plastic bags stuffed with loose receipts" into major news stories became fully apparent only when the Government finally published the expenses claims last week.

It was luck that Winnett took the call when John Wick, the ex-SAS officer handling the disk's sale, rang the Telegraph news desk. Wick had offered the disk to three other papers, but it was Winnett who, after being given the expenses claims of two MPs as a sample, immediately saw its potential and persuaded his editor, Will Lewis, to buy the whole disk. The Telegraph's lawyers have a reputation for caution, but Lewis and Winnett successfully argued that the public interest case was overwhelming.

Once the deal had been clinched, Winnett was given a small team of journalists to help him tackle the blizzard of information. These included Rosa Prince, a lobby correspondent; Christopher Hope, Whitehall editor; Holly Watt, a reporter who joined the paper two months earlier; Jon Swaine, a young reporter who completed the graduate training scheme last year; and Martin Beckford, the social affairs correspondent. Political correspondent James Kirkup was initially on jury service but joined on his return. Andrew Porter, political editor, was left to cover politics from the lobby alone.

Winnett, who joined the Telegraph from the Sunday Times in 2007, could not have been better suited to the task. "Rob is brilliant at getting stories out of very dull spreadsheets," says a colleague. "He can be bothered to trawl through data to find a top story. He is a superlative investigative journalist."

Locked in the bunker, Winnett devised a system for going through the data methodically. First he sliced it up and distributed it between the six journalists, giving himself the Cabinet, somebody else the shadow Cabinet, somebody else Tory grandees and so on. The real work – checking expense claim addresses against the Land Registry, began a couple of days later. This information led the Telegraph team to discover some MPs' habit of "flipping" properties, designating a second home on which expenses could legitimately be claimed then switching to another. Checking electoral rolls and Companies House also revealed that some MPs had been switching second home designations to avoid capital gains tax. A source close to the operation describes the scene as "like the ops room in The Wire. They would pin pictures of their targets on the wall then cross them out in red as they resigned."

Staff not involved in the operation had no idea what their colleagues were up to. "We were all taken by surprise when the story broke," says one. The first clue came at 2:36pm on Thursday 7 May when Beckford tweeted "Daily Telegraph team (including me!) reveals secrets of MPs' expenses."

Sales of the Telegraph shot up, with 93,000 extra copies sold on the first Saturday. For two weeks, none of those involved took a day off. They started at 8am, worked until 9pm, then headed to the bar of the Thistle Hotel where they would watch the 10 o'clock news, the first 20 minutes of which would be dedicated to the next day's revelations.

As the stories were published, the team grew to more than a dozen. "It was like a shadow paper," says a Telegraph staffer. Working full-time on the story in addition to Winnett and his team were: a picture researcher; a sub; a designer; head of news Chris Evans; news editor Matt Bailey; head lawyer Arthur Wynn Davies; deputy editor Tony Gallagher; and Ian Douglas, who loaded the stories on to the web.

Yesterday The Telegraph published the disk in full, closing one of the most exciting chapters in its history. Lewis has drawn much criticism for his editing style, but the operation's ruthless efficiency has forced critics to rethink. "It saddens me to say," says one old hand, "but we wouldn't have done it as well under the old regime."