Prince Charles' supporters have said his reported campaign of letter-writing to ministers shows he is a voice of the people, while opponents have accused him of interfering in affairs that don't concern him.

Labour left-wing MP Dennis Skinner launched a tirade against the prince, challenging him to say whether he had been equally active in writing letters when the Conservatives were in power.

This is someone who was born with a mouthful of silver spoons...who's looking for things to do, so he fires off letters

Ian Davidson MP

Details of Charles' leaked letters to ministers appeared in the Daily Mail, but a spokeswoman for the prince maintained he should have been entitled to confidentiality.

And supporters, including the Tory leader and two royal biographers, insist he has the right to speak out publicly on controversial issues.

'Voice of sanity'

Prince's biographer, Penny Junor, said he was just saying what ordinary people were ''increasingly denied the right to do''.

Penny Junor says prince's intervention makes sense

''He's saying what common sense dictates... he is the voice of sanity in an increasingly insane world,'' Ms Junor said.

''If he has a value it is to speak up for what the rest of us feel powerless to do anything about.''

Ian Davidson, Labour MP for Glasgow Pollock, told BBC Radio 4's Today programme that people should not ''kid themselves that Prince Charles is a representative of ordinary people''.

"This is someone who was born with a mouthful of silver spoons, a mega-wealthy farmer who's looking for things to do, so he fires off letters,'' he said.

Mr Davidson said that if the prince wanted to get involved in politics, he should stand for election.

He's got a right to (comment), some would say a duty

Oxford University Professor Vernon Bogdanor

Conservative Party leader Iain Duncan Smith defended the prince's right to speak out.

''Just like anybody else in this country he can write to a minister and I hope that they write back... but I don't think it helps anybody if somebody just leaks a letter out,'' he said.

Lord Russell, a member of the House of Lords, said the right to advise was ''the central role of monarchy''.

''Part of his role must be to highlight problems and represent views in danger of not being heard,'' his spokeswoman said.

Royal precedents

But Mr Skinner went as far as accusing the prince of following "a right wing" agenda.

He told BBC news: "I want to know from him whether he wrote protest letters to (former Prime Minister Margaret) Thatcher about the Poll Tax. Where was the prince during the great pit strike (of the 1980s) when families were starving?

Dennis Skinner attacked the prince's comments on compensation

''If he did none of those things, then it is pretty clear that he is only writing from a right-wing position.''

Mr Skinner said that during the years of Conservative rule, the prince had occupied himself by ''talking to plants''.

''When (Labour) voted to abolish hereditary peers, he thought he'd better start writing,'' he said.

Constitutional matters

Of the constitutional merit of the prince's actions, Professor Vernon Bogdanor, professor of government at Oxford University, said: "He's got a right to do so, some would say a duty.

''He will become the sovereign. The more he understands about the country, the better for the country.''

Another of the prince's biographers, Jonathan Dimbleby, said Charles was well aware of his role, but that it was right for him to care about "all of our businesses".

He said: "Constitutionally he becomes bound hand and foot and gagged once he becomes king but until then he is a free person who has to think carefully, of course, about how he uses his position.

"A distinction has to be made between the prince's right to speak out in public on matters of controversy and his obligation not to get involved in party political issues and that's a distinction of which he is very much aware."

The Prince of Wales can also point to the fact that such royal correspondence is not new: Queen Victoria's husband, Prince Albert and King George V were two royals who were both highly active letter writers.