The government insisted freedom of information would not be 'a research arm for the media'. So just how useful is it for news?

When it comes to MPs' expenses, how much do we owe to the Freedom of Information Act and how much to a CD of data leaked by an insider? We would never have found out about MPs' practice of "flipping" addresses without the Telegraph's story, certainly. But there are some details – claims for mole clearance, lightbulb replacement and porn videos among them – that stem from FoI requests made in 2005.

Journalists at the The Sunday Times (Heather Brooke and Jon Ungoed-Thomas) and Sunday Telegraph (Ben Leapman) requested information about the expenses of 14 MPs, including Tony Blair and Margaret Beckett. Three years and a high court victory later, in May 2008, Michael Martin, the Speaker of the House, was forced to issue the – albeit rather uninteresting – details. It was another 10 months before Jacqui Smith's domestic arrangements and Tony McNulty's two London homes were revealed, and the public started taking notice.

In the meantime, however, parliament had amended the Freedom of Information Act to prevent MPs' addresses from being revealed. And without the Telegraph obtaining the un-redacted expenses accounts from an insider, we might never have found out, for instance, that the Luton MP Margaret Moran's second home is in Southampton, 100 miles away from her constituency. Or about MPs' penchant for "flipping" properties.

What these discoveries show is that even if FoI has not been proven as a tool of journalism, its power should not be underestimated. While "the government did not introduce freedom of information in order to do something 'for journalism'", according to Lord Falconer, thanks to the initial efforts of Brooke, Leapman and Ungoed-Thomas, those expenses accounts would have been published – minus redactions – by parliament in July.

Lord Falconer is no longer in office and his former Department for Constitutional Affairs no longer exists, but his statement that FoI was introduced "for the public. The job of the government is not to provide page leads for the papers, but information for the citizen" still holds good as an expression of the government's attitude to the act which it introduced.

And yet FoI has yielded important stories. But while one journalist described FoI to me as "the best thing that has happened in my 20 years in journalism", another investigative reporter complained that the law is continually being undermined by the government that brought it in: "The act has so many exemptions that the authorities can always find a reason not to release something."

I started my investigation at the Reuters Institute at Oxford to find out how the act could assist me in my journalism on BBC Radio 4's The World Tonight. Journalists who are prepared to fight for their story through the whole FoI process are a special breed. Even when official information is disclosed promptly, you have to work to a three-month schedule. Going to the information commissioner, if you get turned down, will mean an extra six months before you can make your case. If officialdom won't heed the commissioner, then the gestation period will exceed two years. Many journalists might ruefully agree that Lord Falconer got it right when he went on to comment that FoI "will never be considered to be a research arm for the media".

Not everyone sees it that way. The most prolific user of the Freedom of Information Act in Britain is Matthew Davis, who has created a news agency, Datanews, entirely based on FoI researches. But he too has lost out through delaying tactics in government. His request for a breakdown in the time allocated by Des Browne to his respective duties at the Ministry of Defence and the Scottish Office was accommodated only after the "part-time" defence secretary had left the cabinet.

Are these delays really evidence of news management? One example clinches the argument. In 2005, a Liberal Democrat peer, Lord Avebury, asked for details of the frequency of telephone calls between Tony Blair and Rupert Murdoch in the run-up to the Iraq war. After more than two years' delay and an initial refusal to accept the ruling of the information commissioner, the Cabinet Office published the information the day after Blair stepped down as prime minister. "We decided it was in the public interest" was all officials would offer by way of explanation.

But if FoI requests are becoming too long-winded, or not cost-effective for journalists, there are many others only too willing to help them with free research. The purveyors of "FoI for free" are pressure groups, campaign organisations and political parties. For them, the slog of digging for information, often from large collections of authorities, such as hospitals and health trusts, is well rewarded if the media picks up a story and runs with it.

Matthew Elliott, the chief executive of the Taxpayers' Alliance, has made newsgathering through FoI an integral part of his campaign methods. "What we've tried to do since 2004 is understand how the media works, so we've tried to give news stories to journalists on a plate," he says. "We use the Freedom of Information Act and a team of researchers to get fresh figures from government and local councils, which we package up into brief, media-friendly research papers, complete with eye-catching headline figures to give reporters a ready-made top line."

Regardless of the motivation of those providing the raw material for stories, researches can be objectively assessed: if FoI reveals that the numbers of mixed-sex wards are above government targets, then the integrity of the information stands alone, whatever the affiliations of the researcher.

For all the front-page stories on MPs' expenses, the case for journalism by FoI is still to be made. Cost pressures and time pressures in newsrooms suggest FoI fishing expeditions are likely to reduce. But there is every evidence that the campaigners will take up where journalists leave off. Freedom of information will continue to be a well-exploited right but it would be ironic if it also became predominantly, to paraphrase Lord Falconer, "a research arm for political opponents and pressure groups".

• Jeremy Hayes is senior output editor for The World Tonight. His research paper 'A Shock to the System: Journalism, Government and the Freedom of Information Act 2000' will be published at a seminar at the Reuters Institute for the Study of Journalism on 20 May.