Grand Duke Henri of Luxembourg is to be stripped of his executive power to veto laws passed by parliament after threatening to block a Bill to allow euthanasia in the tiny state.

The hereditary sovereign, 53, who is the last Grand Duke in the world, caused a constitutional crisis when he gave notice that he objected to Luxembourg following its neighbours Belgium and the Netherlands in permitting euthanasia before a second-reading vote in the Chamber of Deputies next week.

Jean-Claude Juncker, the Prime Minister, also opposed the Bill but decided that the Grand Duke had overstepped the mark in threatening to deny the will of parliament.

Mr Juncker will propose a change to the constitution to downgrade the role of the Grand Duke to promulgating laws with his signature rather than approving them, giving him a purely ceremonial duty in line with the other European constitutional monarchies.

Luc Frieden, the Justice Minister, said: “[The Grand Duke] will no longer participate in the legislative process; he will just sign the law to mark the completion of the procedure.”

The Grand Duke, who was trained at Sandhurst, succeeded to the dukedom in 2000 when his father abdicated.

His ethical stance on euthanasia caused the worst constitutional crisis in Luxembourg — which has a population of fewer than half a million — since Grand Duchess Marie-Adelaide was forced to abdicate in 1919 for being too pro-German during the First World War.

The first reading of the euthanasia Bill was approved by 30 votes to 26 in February and the intervention by the Grand Duke was seen by some as an attempt to influence the final vote.

Mr Juncker said: “I understand the Grand Duke's problems of conscience. But I believe that if the parliament votes in a law, it must be brought into force.”

The only other time that a sovereign has blocked a law was in 1912, when the Grand Duchess Marie-Adelaide refused to sign an education Bill.

François Bausch, the leader of the Green party, which supported the euthanasia Bill, said: “I hope the law will pass through Parliament by the end of the year. I hope that the Grand Duke will respect the consensus which has always prevailed in Luxembourg.”

Privilege and power

— In Europe there are only 12 monarchies left, including seven kingdoms and the elective monarchy of the Vatican

— Juan Carlos of Spain became King upon Franco's death in 1975. He supported a move to strip much of his own power

— Queen Beatrix is a member of the Government and a head of state in the Netherlands

— In 2001 ex-King Simeon of Bulgaria became Prime Minister

Source: Times archives

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