Leading article: The cost of dissidence

Prince Charles's decision to take legal action against The Mail on Sunday for publishing one of his journals is the latest in a long line of embarrassing blunders by the hapless heir to the throne. It was the Prince's choice to vouchsafe his "private" thoughts to as many as 100 confidants. It was naive of him to imagine that they would not eventually see the light of day, particularly if they contained controversial remarks.

So we have little sympathy with the Prince for the situation in which he now finds himself. The details that have emerged reveal how he has repeatedly used the media for his own ends. Since he has had no compunction about leaking information to the press when it has suited him, he cannot reasonably hide behind the confidentiality laws now. The farce being acted out in the High Court is a shameless attempt by the Prince to have it both ways.

But this case has also revealed something more worrying than the Prince's hypocrisy. His former deputy private secretary Mark Bolland has revealed in a witness statement that Prince Charles sees it as his role to "influence opinion" and likes to think of himself as a "dissident" who goes "against the prevailing political consensus".

This tragi-comic description rings horribly true. We already know that Prince Charles has a habit of writing to ministers to air his views. The Lord Chancellor once complained of being "bombarded" with letters from the Prince. On top of this, we now learn that Prince Charles sees himself as some sort of political activist. This is dangerous ground.

Britain's constitutional monarchy survives on an unwritten understanding that the sovereign will not get involved in politics. Yet Prince Charles has shown no sign that he appreciates this. His statements are encroaching ever more brazenly on to political territory: education, science, the environment are among recent topics he has raised. The Prince's aides stress that he will be less vocal when he becomes King, but by then it will be too late. And in truth, he has demonstrated little capacity for self-restraint thus far.

The constitutional role of the Crown still matters. It is the sovereign who invites party leaders to form a government. It is the monarch who must read out the speech setting out the Government's legislative agenda at the opening of Parliament. We must now consider the constitutional implications of a future King Charles openly disagreeing with the policy of the government of the day.

Prince Charles considers himself a dutiful man. Yet his behaviour is jeopardising the monarchy. If he wants to continue as a political "dissident", he must accept that the price of that might - in the end - be his throne.