When President George Bush nominated Samuel Alito to the Supreme Court he was billed as an arch-conservative. But in his first decision last night, the new justice confounded expectations by voting to stay an execution in Missouri.

A few hours after being sworn in at the White House, where Mr Bush praised him for his "steady demeanor, careful judgment and complete integrity," Justice Samuel Alito joined the majority in a 6-3 vote to block the execution of Michael Taylor, a murderer, by lethal injection.

The decision will allow an appeals court to hear arguments by Taylor's lawyers that all executions by lethal injection are unconstitutional. The US Constitution prohibits "cruel and unusual punishment". Lethal injections sedate prisoners before collapsing their lungs and stopping their hearts.

It was not the decisive vote but it may be a sign of things to come. As well as helping to clear the way for a legal challenge to the preferred method of execution in America - of the 38 states that allow capital punishment, 37 use lethal injections - Mr Alito's decision was an early foretaste that he may not, as anticipated, decisively swing the Supreme Court to the right.

Mr Alito, 55, was confirmed as Mr Bush's second appointment to the court by the Senate on Tuesday after bitter and partisan series of hearings that explored his judicial career and tried to elicit his ideological bearings. During his re-election campaign in 2004, Mr Bush promised to appoint conservative jurists to the Supreme Court.

Mr Alito, dubbed "Scalito" in honour of Justice Antonin Scalia, the most outspoken and conservative member of the court, replaced Justice Sandra Day O’Connor, a moderate who was often the swing vote on the nine-member court. In 1985, Mr Alito said he was "particularly proud" of crafting an argument that opposed a woman's right to abortion.

His first Supreme Court vote came at the end of a long first day in the court. Despite not yet having an office, Mr Alito rushed from the White House to hear three last-minute death penalty arguments. In the first two cases - one of which was a separate appeal by Taylor - he abstained, but on the third, he cast his first vote.

In supporting the majority, Mr Alito opposed Chief Justice John Roberts, Mr Bush's first appointment to the court, and Justices Clarence Thomas and Antonin Scalia, conservative heayweights who routinely allow executions to go ahead and criticise lengthy delays in death penalty cases.

Missouri had set an execution date of midnight last night (5am GMT) for Taylor's execution. He was convicted of kidnapping, killing and raping Ann Harrison, a 15-year-old girl, in 1989. Taylor pleaded guilty but said he was high on crack cocaine at the time.

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