The SNPs constitutional affairs spokesperson Tommy Sheppard MP had sent a Freedom of Information request in June 2019 seeking information on polling since January 2018 on public perception on the Union and how much money had been spent on it.
After the Cabinet Office refused, the SNP MP appealed to the Office of the Information Commissioner, arguing that since the UK Government had no stated intention to review or alter policy in respect of the Union, the clause should not apply.
Now the First-tier Tribunal Information Rights have ruled the information requested “relates to the implementation of existing policy rather than to policy development” and the Cabinet Office must disclose the information within 28 days.
The ruling said there was a “clear public interest in seeing what information the Cabinet Office is using to assess public attitudes to the Union”, as well as in “understanding more about any analysis the Cabinet Office is undertaking regarding the strength of the Union”.
It added there was a public interest “in transparency regarding the use of public funds”, and in knowing more about what the money paid for.
The Cabinet Office had also argued that as Mr Sheppard's request was three days after they received the polling information, they had not had enough time to analyse it.
However, the tribunal ruled that arguments about timings were "not a matter which impacts on our deliberations".
Responding to the verdict, Mr Sheppard said: “This is a very welcome decision with significant consequences.
“The Cabinet Office has been hiding this data claiming that they were developing policy.
“I have been clear from the start that this wasn’t the case – maintaining the Union is clearly an ongoing policy of the UK Government – and the tribunal has come to the same conclusion.
“We have the right to know how much of taxpayers’ money has been spent on it, and what the polling says.
“I have long suspected that the UK Government is determined to keep this polling secret because the results make uncomfortable reading for them and show widespread and engrained support for political control coming back to Scotland through independence.”
The Cabinet Office has been approached for comment.