Veto over Prince Charles letters based on value judgment, court told

Government lawyers have defended a decision by the attorney general, Dominic Grieve, to block the publication of letters written by Prince Charles to politicians.

Grieve overruled an independent freedom of information tribunal that had ordered the release of the letters. The tribunal had decided that the public should be told how the prince sought to influence government policy through private letters he sent to ministers.

The government has spent nine years resisting the disclosure of the letters, which it concedes contain the prince's "most deeply held personal views and beliefs".

On Tuesday, in the latest stage of the long-running battle, government lawyers at the court of appeal sought to justify the use of a veto by Grieve to overrule the tribunal.

Grieve's veto banned the disclosure of 27 pieces of correspondence between the prince and ministers in seven government departments between September 2004 and April 2005.

Jonathan Swift, the QC for the attorney general, told the court that Grieve "was entitled to take a different view on matters of public interest from the tribunal, without any requirement for fresh evidence or a material error of fact".

The Guardian, which requested the correspondence under the Freedom of Information Act in 2005, is seeking to overturn the veto and see copies of the letters that Grieve says contain the prince's "particularly frank" views.

This week's case at the court of appeal is the latest round of a tussle that has already been played out at hearings at the high court and the freedom of information tribunal, and in an adjudication by the information commissioner.

Meanwhile, the government has delayed disclosing how much money it has spent in legal costs to ensure the letters remain concealed from the public.

In a further freedom of information request two months ago, the Guardian asked the attorney general's department and the Treasury solicitor's department how much money they had spent on barristers and lawyers to oppose the publication of the letters.

The Freedom of Information Act requires government departments to respond within a month. Last week the two departments said they needed more time to decide whether to release the information.

Swift told the court of appeal that Grieve had reasonable grounds to overrule the freedom of information tribunal.

"His disagreement with the tribunal was about the weight to be accorded to various competing public interest factors, rather than about matters of primary fact or pure law," he said. "It was a value judgment on matters which (given their constitutional and political overtones) could fairly be said at least in practical terms to lie within the domain of government ministers."

Grieve's reasons were "proper, rational and made sense. The fact that he reached a contrary conclusion to the tribunal did not mean that his conclusion was improper or unreasonable," he argued in front of the master of the rolls, Lord Dyson, and two other judges.

When Grieve issued his veto in October 2012, he said there was a risk that the prince would not be seen to be politically neutral if the letters were read by the public.

He said: "This risk will arise if, through these letters, the Prince of Wales was viewed by others as disagreeing with government policy. Any such perception would be seriously damaging to his role as future monarch because if he forfeits his position of political neutrality as heir to the throne he cannot easily recover it when he is king."