Freedom of information (FOI) should not be seen as a threat by public sector bodies, the UK information commissioner, Richard Thomas has urged.

But in a keynote speech to the Freedom of Information Live information rights conference in London, the information watchdog added that individuals using the Freedom of Information Act should "act responsibly."

Thomas told the public sector audience that freedom of information reinforced good government. "Some people fear that FOI can have a 'chilling effect' and that nothing gets written down," he said.

"On the contrary – the possibility of disclosure encourages a record of full, accurate and impartial advice from civil servants and supports the principle that officials advise and ministers decide. Greater openness will deter spin and informal decision making."

Earlier this month, Thomas scored a victory when the Information Tribunal, which hears appeals against decisions made by the Information Commissioner's Office, upheld his original ruling and ordered the government to publish "gateway reviews" on the progress of the £5.5 billion ID card scheme.

The decision had been resisted by the Office of Government Commerce, which carries out the reviews of major public sector projects.

Thomas warned public bodies that public interest arguments for nondisclosure must be convincing in each case. There were "bound to be times when the Freedom of Information Act may be uncomfortable," he said.

Openness meant treating citizens "as grown ups" and reflected the realities of public life. "People respect honesty, not cover up," he said.

But the watchdog added: "Wresting information from government and other public bodies has the potential to damage trust between the state and the people. But, by the same measure, those making requests must act responsibly and with restraint."

The Act was delivering "real benefits" after two and a half years in operation. "It is now recognised as a key feature of our modern democracy which is changing public sector culture," he said.

"There is a presumption of disclosure, unless there is a genuine reason to withhold information. This must trump any instinct of unnecessary secrecy which simply suggests a public authority has something to hide."

The Information Commissioner's Office is developing guidelines to help public bodies resist requests that are genuinely vexatious, with a "Charter for responsible FOI requests."

Thomas said: "I am sympathetic towards public authorities that refuse to deal with vexatious requests which clearly serve no reasonable purpose. Such requests do a disservice to all who want freedom of information to be a success."