Prince Charles should be permitted to lobby ministers, Nick Clegg has said, as campaigners' concerns about royal activism intensify.
The deputy prime minister was asked about the issue on LBC this morning, but he rejected criticisms that the heir to the throne had acted improperly after it emerged he lobbied New Labour ministers on issues like grammar schools and GM food.
"This idea that just because you're a member of the royal family you don't have opinions just seems to me silly," he said.
"It assumes to me the idea... the politician will automatically do what is said. That's simply not the case."
The BBC documentary The Royal Activist revealed that Labour ministers Michael Meacher, Peter Hain and David Blunkett were relaxed about the prince's interventions.
But news of his interest prompted criticism from some quarters.
Graham Smith of Republic told Politics.co.uk: The implied deal with the public is the monarchy is acceptable because it doesn't get involved in politics. People will take a different view about the monarchy if they think Prince Charles is breaking that deal.
Smith accused Clegg of "attempting to rewrite our constitution and wind the clock back 300 years".
He added: "It is a constitutional fact that royals are not allowed to get involved in politics. If Nick Clegg wants to change that, we've got a problem."
Despite the concerns Clegg has made clear he does not believe there is a problem with Prince Charles' activities.
"Constitutional monarchy means exactly what it says on the tin - that the limits of the decision-making executive power of the royalty are clearly confined, but that doesn't mean you can't express opinions," he added.
"I think as far as politicians are concerned they should do what they are elected to do - represent the public, act in the national interest and listen to views from a whole range of people. That's what a democracy's about."
The Liberal Democrat leader refused to reveal whether he had ever faced pressure from the Prince of Wales, continuing the lack of transparency which has only served to exacerbate suspicions of royal influence.
The long-running legal battle over the Prince's 'black spider' letters - so-called because of his style of handwriting - has seen Clarence House attempt to block the publication of the correspondence.
Spinwatch's Tamasin Cave told Politics.co.uk: "Ministers should really be taking advice from people who are best-placed to give it.
"Prince Charles, if you strip away all the paraphernalia of royalty, is a businessman with multimillion pound business interests.
"When you have people with commercial interests interfering in policy, there needs to be maximum transparency. I wouldn't make any distinction between Prince Charles and his business interests and any other powerful person in this country. If they are speaking to ministers, the public must know.
"If they're going to be talking to people, they need to say who they're talking to and what they're talking about so the public can scrutinise who's having influence over policy."