How much should you know about Prince Charles's attempts to change government policies? Since 2005, the Guardian has fought to make public letters sent by the prince to Whitehall ministers. No one disputes that these "black spider memos" are important and of public interest. Last autumn, a Freedom of Information tribunal of three judges ruled that they should be published for "transparency as to how and when Prince Charles seeks to influence government". Even as he vetoed the judges' decision, the attorney general, Dominic Grieve, admitted that the "advocacy correspondence" showed the prince disagreeing with government policy. But to preserve the fiction that the future monarch is politically neutral, Mr Grieve demanded the letters be kept secret.

Without even consulting parliament, a cabinet minister has overturned a court verdict – and put his hand over the public's eyes to shield it from unpleasantness. Today three senior judges admitted that they found the block "troublesome". The veto's very existence, said the lord chief justice, was "a constitutional aberration". The judges went on: "It is not quite a pernicious 'Henry VIII clause', which enables a minister to override statute but, unconstrained, it would have the same damaging effect on the rule of law." Yet having painted the veto as indefensible, the judges then elected to uphold it. Eight years later, and despite a landmark ruling by an FoI tribunal, members of the public are still no closer to seeing how the Prince of Wales tries to influence governments they have elected.

For, make no mistake, this is meddling of the highest order. Government advisers have described in court how such royal memos went to the "top of the pile" and were "treated with great reverence". The prince's interests are wide-ranging – the letters in question were sent to seven Whitehall departments, from the Department for Business to the Northern Ireland Office – and he has been enthusiastic in pursuing them, writing 27 letters in just seven months between 2004 and 2005.

To be clear, this correspondence was not about routine engagements or part of the prince's preparation for kingship, which would place them outside publication under the Freedom of Information laws (which have since been restricted further to exempt all Prince Charles's correspondence). By Mr Grieves' own admission, these are "particularly frank" letters by which Prince Charles seeks to influence public policy. Yet Britons are not permitted to find out the nature of that influence: what has been demanded or what has been given. It is obvious what the public loses by such secrecy. It is less clear how much Clarence House really gains by having the vacuum filled with partial leaks and innuendo. The shroud should not be left in place.