A national newspaper is to challenge two central tenets of the hereditary British monarchy under the Human Rights Act.

The Guardian claims the Act of Settlement - which bars non-Protestants, adopted children and people born to unmarried parents from succeeding to the throne - must be brought in line with European human rights laws.

The newspaper wants the removal of what it says are anomalies and for a reinterpretation of the 1701 law - which the paper says also discriminates against women by favouring male succession.

The Guardian has even placed advertisements in the German newspaper Suddeutsche Zeitung, calling on German blue bloods to join the legal action.

We very much hope that the odd Hapsburg or Saxe-Coburg might join in

Guardian editor, Alan Rusbridger

The adverts say dozens of Germans have been excluded from the succession.

Guardian editor Alan Rusbridger said: "We very much hope that the odd Hapsburg or Saxe-Coburg might join in."

The paper will also argue that the Treason Felony Act - forbidding the publication of incitements to republicanism - contravenes Article 10 of the European Convention, which guarantees the right to free speech.

Parliament could face condemnation from the European Court of Human Rights if it issues a "declaration of incompatibility" and refuses the changes.

Geoffrey Robertson QC will spearhead the case for the paper.

Mr Rusbridger said: "No one can really defend an Act which forbids Catholics from becoming a country's head of state.

Rusbridger: "The monarchy will end"

"But, though even the Archbishop of York has suggested the Act of Settlement is reformed, no one has done anything.

"Since MPs are barred from openly debating the role of the monarch we thought a newspaper might set the ball rolling."

Speaking on BBC Radio 4's Today programme, Mr Rusbridger said people were wary of debating the issues because they "don't know where it will stop".

But, he added, the monarchy would end one day, "and we should be able to vote on it."

'Think of the alternative'

Joining the debate, Conservative peer Lord Onslow dismissed The Guardian's campaign as "an extraordinarily good piece of advertising".

"You've got to think of the alternative," he said in defence of the Royal family. "The idea of Mrs Thatcher trotting up the Mall with an escort of the Household Cavalry is bizarre," he told Today.

Criticising The Guardian's call for a vote on the future of the monarchy, the peer said: "Napoleon became emperor by plebiscite. I'm not totally sure they're a good thing."

Salmond: "Discrimination unacceptable"

The newspaper's legal challenge comes as a Guardian/ICM poll of 1,003 people indicates that 66% think the ban on Catholic succession should be lifted, while 63% disapprove of the ban on children to unmarried parents, and 68% on adopted children.

A total of 60% say they would prefer to be citizens than royal subjects and 30% think there should be a vote on who should succeed the Queen when she abdicates or dies.

Former SNP leader Alex Salmond MP welcomed the action.

"Exactly one year ago, the Scots Parliament - on a motion from the SNP - unanimously passed a resolution calling for repeal of this discriminatory piece of legislation, but the House of Lords supported it remaining in place," he said.

This 18th-Century relic has no place in the 21st Century

Alex Salmond MP

"This 18th-Century relic has no place in the 21st Century.

"It is high time that the Westminster Parliament recognised that any form of religious discrimination is no longer acceptable."