Five years ago, the National Council for Voluntary Organisations published a report that found charities were not making enough use of the Freedom of Information Act.
The act, introduced in 2000, gives everyone the right to request information that is held by public bodies.
It has proved tremendously powerful for some organisations and individuals. Yet charities' failure to use it widely prompted the NCVO to publish its own guide last month.
Voicing Your Right to Know: A Guide to Using the Freedom of Information Act in Campaigning says FoI requests can have a "transformative effect" on campaigning.
"FoI can be extremely cost-effective - at the cost of writing a letter it can transform a campaign in its foundation, through content, and in its reach, through advocacy," the guide says.
The 51-page guide includes case studies of charities that have used the act. Some encountered difficulties, as the special-care baby charity Bliss did when it sent requests to neo-natal units nationwide for information about whether hospital units were meeting care standards.
It received a 92 per cent response rate, but some paediatricians the charity worked with thought the approach was heavy-handed. All the organisations in the case studies felt the effort was worthwhile, however. The autism education charity TreeHouse used a PR company to handle its FoI request, which asked the head of children's services in every local authority for details about their provisions for children with autism.
Sixty-two out of 200 requests were answered and the data was used in Snapshot, the charity's 2009 report of children's autism services in the UK.
The Campaign for Clear Air in London asked the Mayor of London's office how the official number of 1,031 premature deaths in the capital in 2005 caused by dangerous airborne particles was calculated. It received lots of stonewalling, but the publicity raised its profile considerably.
Simon Birkett, founder of the campaign, says in the guide that the act had "fundamentally changed" what its campaign had been able to achieve.
But some charities do not understand that the requests are free and easy to submit, according to Susie Rabin, campaigning effectiveness manager at the NCVO. The most important thing to remember when considering whether to submit a request is the wording, she says.
"Make sure you frame your request appropriately," she says. "Ask for specific information over a specific time period rather than something that can be interpreted vaguely."
She says charities should also consider how much time they are prepared to invest in their requests - public bodies are often reluctant to release information, which can lead to appeals, which may take months.
But she says smaller charities in particular should make greater use of the act. "Some people just aren't aware of it and it can be a frustrating experience," says Rabin. "But most people are happy with the responses they get. For a small amount of time and input, you can get a lot of information."