The Attorney General wrongly overrode the decision of "an independent and impartial tribunal" when he blocked public disclosure of letters the Prince of Wales wrote to Government ministers, the High Court has been told.
The claim was made yesterday at a hearing at which Guardian newspaper journalist Rob Evans is attempting to overturn Dominic Grieve's controversial decision last October to veto the release of correspondence between Charles and seven Government departments.
Evans' application for judicial review is being heard over two days by the Lord Chief Justice, Lord Judge, with Lord Justice Davis and Mr Justice Globe.
Grieve, the Government's principal legal adviser, said his decision was based on his view that the correspondence was undertaken as part of the Prince's "preparation for becoming king".
Making the letters public could potentially damage the principle of the heir to the throne being politically neutral, and so undermine his ability to fulfil his duties when king, he said.
But Dinah Rose QC, appearing for Evans, told the High Court yesterday that Grieve had made errors of law and his decision must be quashed.
The Government had been ordered to disclose letters sent by Charles during a seven-month period in 2004 and 2005 after Evans won a
freedom of information appeal.
A freedom of information tribunal had ruled in favour of Evans, who had challenged a decision by the Information Commissioner to uphold the
refusals by Government departments to release the correspondence.
The tribunal ruled that Evans was entitled to "advocacy correspondence'' – described described as letters seeking to advance the work of charities or to promote views – written by Charles.
But Grieve issued a certificate vetoing disclosure under section 53 of the Freedom of Information Act 2000 and under the Environmental Information Regulations 2004.
Rose argued that section 53 could not lawfully be used in respect of environmental information because "the exercise by the executive of that
power to override the decision of an independent and impartial tribunal" was incompatible with EU law.
The error had also led Grieve wrongly to apply section 53 "to the entirety of the information" which was the subject of the disclosure
request when he had "no power to prevent all the correspondence falling into the public domain".
The Attorney General's legal team argues that his decision to issue the section 53 certificate "was plainly a decision that was open to him"
after he "disagreed with the tribunal's assessment of the relevant public interests".
In a written statement last year Grieve said: ''I consider that such correspondence enables the Prince of Wales better to understand the business of government; strengthens his relations with ministers; and enables him to make points which he would have a right – and indeed a duty – to make as monarch.''
He added: ''If such correspondence is to take place at all, it must be under conditions of confidentiality. Without such confidentiality, both the Prince of Wales and ministers will feel seriously inhibited from exchanging views candidly and frankly, and this would damage the Prince of Wales' preparation for kingship.''
The seven Government departments to which the Prince wrote were Business, Innovation and Skills; Health; Children, Schools and Families; Environment, Food and Rural Affairs; Culture, Media and Sport; the Northern Ireland Office and the Cabinet Office.
Making his announcement last year Grieve said his decision to "exercise the veto in this case was not taken lightly".
He said he had taken into account the views of the Cabinet, former ministers and the Information Commissioner "in considering both the balance of the public interest in disclosure and non-disclosure and whether this is an exceptional case".
Grieve said: "My view is that the public interest favours non-disclosure. I have also concluded that this constitutes an exceptional case and that the exercise of the veto is warranted."
Rose said in written argument before the court that the Attorney General had "adopted an impermissible blanket approach, unreasonably failing to consider the public interest balance in respect of each individual piece of correspondence".
She said: "Even if there are particular sensitivities arising from particular letters or passages within them which would entitle the defendant (Attorney General) to hold, on reasonable grounds, that they are exempt from disclosure, it is highly unlikely that such sensitivities apply across the board."
Rose submitted that the Attorney General should have "applied his mind to each item separately so that letters or passages in respect of which there is no overwhelming public interest against disclosure" should be communicated to Evans.
The court was expected to reserve its decision.