Departments led by Tory leadership hopefuls Rishi Sunak and Liz Truss were the least transparent in the entire government last year, openDemocracy can reveal.

The Treasury refused to comply with more Freedom of Information (FOI) requests than any other department in Whitehall while Sunak was chancellor.

And the Foreign, Commonwealth and Development Office (FCDO), where Truss took over as secretary of state in September, was the slowest of the government’s 41 departments and agencies at releasing information.

The two leadership hopefuls have repeatedly come under fire for secrecy, with one MP branding the pair “appalling”.

The SNP’s Tommy Sheppard said: “Their stance on FOI is awful.

“They are both appalling in every other respect, so it doesn't surprise me that they're also dreadful at transparency. Boris Johnson set a pretty low bar, but they seem determined to get under it.”

In May, equality campaigners reacted with anger after the Treasury refused to release information showing what impact Sunak’s spending decisions would have on disabled people.

He was also criticised for refusing to “come clean” about the costs of a controversial plan to create an NFT (non-fungible token) backed by the British state.

In total, more than half of the FOI requests sent to Sunak’s team last year were rejected – and just one in five led to a full response.

Meanwhile, the FCDO has used a legal loophole to conceal its delayed response in the official figures, which openDemocracy revealed last year.

Under Freedom of Information law, authorities have 20 working days to answer a request. But they can postpone this deadline for as long as they want, simply by claiming they are “considering the public interest”. These responses are then considered to be “on time”, even if they arrive months late.

Figures show that the FCDO applied the public interest ‘loophole’ to a record-breaking 30% of all FOI requests it received last year.

But officials have continued to use it. In one case, Truss’s team has repeatedly delayed an FOI request from openDemocracy regarding Russian oligarchs trying to escape sanctions. The FCDO has still failed to respond after sitting on it for 11 weeks.

The department says it needs “more time to consider the balance of public interest in disclosing the information”.

The Department for International Trade (DIT) was the second most prolific user of the ‘public interest’ loophole, applying it to more than one in five requests. Both departments were led by Truss in 2021 – she was promoted from trade secretary to foreign secretary in September.

An independent cross-party commission recommended closing the ‘public interest’ loophole in 2016, but no action was taken by the government.

Both Truss and Sunak have also kept their official diaries secret, despite a long campaign by openDemocracy for transparency.

The Tory leadership hopefuls were accused of trying to cover up “basic facts” about their work in government by refusing to publish details of their meetings, with officials at Truss’s old department saying our requests for transparency were “vexatious” and a “fishing expedition”.

They added that it would not be in the public interest to say who Truss met and spoke to.