"About every 10 years," says David Leigh, The Guardian's investigations editor, "I take on something big."
And investigations don't come much bigger than the one he and reporter Rob Evans have been embroiled in for the past five years.
The pair, who were commended at this year's British Press Awards, have uncovered evidence that Britain's biggest arms manufacturer, BAE Systems – the fourth-largest company in the world – has been paying illegal kickbacks worth hundreds of millions to members of the Saudi royal family and countless "middlemen" around the world, to preserve lucrative arms deals.
They have previously reported that in the now infamous al-Yamamah arms deal, first negotiated by Margaret Thatcher in 1985, BAE inflated prices for fighter jets by 32 per cent when selling to Saudi Arabia to allow for an extra £600m in commissions – £60m of which went into a "slush fund" that paid for cars, planes, shopping and girlfriends for Prince Turki bin Nasser, the Saudi Prince Sultan's nephew, whenever he visited the West. BAE has always denied any wrongdoing.
But the biggest revelation came last month when Leigh and Evans claimed that Saudi Prince Bandar had received £1bn in payments from BAE as part of the al-Yamamah deal.
And they used the occasion to launch a specially designed section of the Guardian Unlimited website, The BAE Files. Leigh says that when the pair started their investigations into allegations of corruption in the arms trade in 2003, no other paper followed up their claims. Over time, even The Guardian newsdesk became less enthusiastic. But the latest revelations have been widely followed up – and have prompted frontpage stories in other national titles.
Leigh says he considered writing a book, but The Guardian editor Alan Rusbridger persuaded him "books are old thinking – let's do a website".
Leigh says: "We started off with a series about how corrupt the business was. Whistleblowers started coming forward, we kept writing about it and no one wanted to know.
No other newspaper took it up, our own paper got a bit bored of it from time to time, but to give it credit it did run it. But now it's taken off, it's everywhere. All the time we've had this battle with BAE, and they've been saying 'piss off, we're this big corporation and nobody listens to you lot, there's no evidence anyway'.
"We were able to lay everything out with no constraints of space and say 'OK guys, here's all the evidence'."
Evans says that he decided early in the project that it doesn't matter where the story goes in the paper, as long as it goes online and reaches a global audience. He says: "It's taking a very long-term view, which editors don't normally take: you put something out there and 18 months later it will suddenly click."
The BAE investigation is now being followed by journalists in dozens of countries – the BAE Files website's interactive investigation map shows just how global the investigation is. Leigh and Evans themselves have travelled all over the world chasing BAE's paper trail, including visits to Tanzania, Romania, the Czech Republic, Switzerland and Sweden. As Leigh puts it, "you've got to take a lot of planes to do a story like this".
The pair openly welcome help from journalists around the world and give it freely to anyone willing to take the story on – even their Fleet Street rivals. One of the most striking parts of the website is how their evidence is published for all to see –memos, faxes, emails and research passed on to them by other journalists and authors working on the story.
"We're trying to think our way towards a new kind of journalism,"
says Leigh. "Everybody says the internet is a new world with citizen journalism, a global audience and everybody having their say, and we tried to do it that way and say 'this is a new kind of journalism and we will put everything in front of everybody'.
"The thing is," he adds with a smile, "all the criminals are global now, the police forces are gradually starting to go global and now the journalists are global as well. We need to catch up."
Investigative journalism has long been described as in decline or waning in importance.
But, for Leigh and Evans at least, online tricks such as graphics, video and audio can give it a whole new lease of life. "Things such as maps and graphics really bring it alive," says Leigh. "The problem with all these bribery and corruption stories is they are often quite complicated, financial and dry. Because of the legal problems, of which there are many, you have to be quite roundabout with the things you say. But to find ways of doing it online that can bring it alive for people and give them a handle on it is a really exciting thing. You've seen these stories which say 'Complex web of financial transactions', and people's eyes glaze over. This is about trying to find a way past that."
Leigh, who was a producer at seminal ITV investigation programme World in Action, believes that news - papers and TV news networks are now attempting to "colonise the same space" online, but the duo rejected the idea of presenting clips themselves, in the style now adopted by many regional and some of the national newspapers.
"One thing we looked at, what The New York Times does, is to have video clips of their reporters doing clips to camera, which I think looks naff. The Financial Times is doing it now too. I don't think that's playing to our strengths; it looks like cheap TV."
That is not to say that The Guardian is not keen on video. Having just appointed Robert Freeman from the Press Association as head of video, and invested in video training for its picture desk as well as broadcast-quality cameras, Leigh and Evans hope to film more interviews for The BAE Files.
Evans says the clip of Prince Bandar replying to allegations of corruption with the words: "So what?... We didn't invent corruption", is "worth a thousand words".