Editors of UK national newspapers are calling on the government to protect the Freedom of Information Act following criticism that the public are being unfairly obstructed when they seek to scrutinise the work of official organisations.

Six editors at papers ranging from the Daily Telegraph to the Mirror have signed an open letter coordinated by openDemocracy requesting an urgent investigation into the act amid fears that the public are being stonewalled.

Last November an openDemocracy report accused ministers of running an “Orwellian unit” at the heart of government that sought to control the release of potentially embarrassing information. It said Whitehall departments were rejecting requests at the highest rate since the introduction of the act 20 years ago.

In the letter, the editors raise serious concerns about the difficulties that journalists and the public experience when trying to use freedom of information legislation across government to request information from official files.

Among the editors to have signed the letter are Katharine Viner of the Guardian, Roula Khalaf of the Financial Times and Chris Evans of the Daily Telegraph. The letter is also backed by a number of former Fleet Street editors including Paul Dacre, who edited the Daily Mail for a quarter of a century, and by academics and lawyers.

They call for measures to speed up official responses to freedom of information requests by the public and a strengthening of the information commissioner, the body that regulates the act.

The editors say the act “is a critical tool for ensuring that journalists and members of the public can scrutinise the workings of government. We have, however, become increasingly concerned about the way in which the legislation is being interpreted and implemented.”

Drawing on the conclusions of the openDemocracy report, they point out the “increasing evidence of poor practices across government”, such as failing to respond to requests.

They criticise the operation of the FoI clearing house, a little-known unit within the Cabinet Office that requires Whitehall departments to send it requests that are deemed to be potentially sensitive or too expensive to answer. The unit routinely instructs departments to send it drafts of proposed responses so that they can be vetted.

“This raises serious questions about whether information requests by journalists and researchers are being treated and managed differently,” the editors write.

According to the openDemocracy report, the budget of the Information Commissioner’s Office, the regulator tasked with implementing freedom of information legislation, has been cut by 41% over the last decade at a time when its caseload has increased by 46%.

Viner said: “At a time when journalistic freedom is under threat around the world, the government’s time-wasting over legitimate FoI requests is at odds with its global commitments to press freedom. Given the huge amounts of public money now spent with private contractors, a clear commitment to greater transparency and a well-funded information commissioner are manifestly in the public interest.”

John Witherow, the editor of the Times, said: “Transparency is not a privilege or a gift bequeathed to a grateful citizenry by a benign government. That message has failed to get through to the government of Boris Johnson, which seems hellbent on making it harder. This is not only a disgrace but a mistake.”

A government spokesperson said the clearing house had operated for 15 years to ensure a consistent approach to requests for information.

“This is especially important for complex FoI requests where we must balance the need to make information available with our legal duty to protect sensitive information and national security,” they said. “This government remains fully committed to its transparency agenda, routinely disclosing information beyond its obligations under the FoI Act, and releasing more proactive publications than ever before.”