Every story is different but when setting out on an investigation there is a series of steps we follow in order to establish the truth and to find the evidence to prove it.
We act on tip-offs, follow any leads that preliminary research throw up, gather all the evidence we can to prove the story is correct and then present the allegation to whoever we are accusing of wrongdoing.
If you would like more detail about the process we go through in bringing investigative stories to air then read on.
If you know of a story you think Newsnight should investigate, please e-mail us at
A tip off can be an anonymous call, an e-mail, a message from a victim perhaps, or a campaigner or lawyer.
Actor Richard E Grant tipped off Newsnight about conmen who were trying to flog a bogus Aids cure in Africa.
Sometimes the tip-off may not be accurate but may still lead in the right direction.
The ideal tip-off comes from a whistleblower who can provide full documentary evidence and eye-witness accounts from the inside.
So how do we extract the nuggets of truth from a garbled account, a suspicion or a hunch?
In the early stages we scour all available sources of basic information - newspaper cuttings, legal databases and Google. We talk to the experts in that field. We put any names we find through electoral rolls, directory enquiries etc.
Some stories stand up. Others fail to make the cut at this early stage.
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This is where the real slog happens. It is time consuming and can be tortuous and ultimately fruitless.
We go all out to get documents: inside documents. These throw up more names to chase. They in turn give you more leads to follow.
We also put in freedom of information requests. You do not have to be a journalist to use FOI. Here is the BBC's guide to help you:
Freedom of Information Guide
Sometimes expert analysis of financial documents can reveal the full story. That is how we discovered that two years after the Asian Tsunami disaster £1bn was sitting unused in Red Cross accounts while victims were still in temporary accommodation.
In some of the murkier areas - crime and intelligence, for instance - confidential sources are essential.
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You may have a blinding story, but you cannot broadcast it on TV unless you can illustrate it. You need evidence.
As in all journalism, getting eyewitness accounts of what happened is essential. Another technique is to collect samples and put them through laboratory tests to check for contamination or DNA traces.
We normally need evidence of apparent criminal or antisocial behaviour before the BBC allows journalists to use secret recording or filming. We can use one or more cameras concealed in a room or hidden in clothing.
One such camera captured illegally logged timber from rainforests being used to refit the House of Commons.
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Before we broadcast an investigation we always put our allegations to whoever we are accusing of unjust, illegal, antisocial or immoral behaviour.
Sometimes they are prepared to brief us even if they will not do an interview. On other occasions people agree to talk on camera but then they change their minds.
If we cannot get a straightforward interview for any reason, the BBC may allow us to do a "doorstep", so-called because they often take place as the subject of the investigation emerges from their house or office. We have to satisfy the BBC that a doorstep is in the public interest.
Take the case of "Goldfinger": the Vulture Fund chief who we caught up with. He had refused all requests for interview on what world leaders had agreed was an immoral trade.
Sometimes it is appropriate to set up a more elaborate sting.
Then it is a matter of getting the investigation onto air. We may be faced with a barrage of lawyers' letters demanding that we do not broadcast the evidence we have found of wrongdoing or we will be sued for libel.
On Newsnight we expect this kind of response, so we try to make our films "bulletproof". We have to get our facts right. We involve our lawyers and the BBC's Editorial Policy unit.
They act as a sounding board so producers can double check they meet the BBC's high standards of conduct, set out in the corporation's BBC's Editorial Guidelines .
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