ALEX Salmond's claim that an independent Scotland would automatically be a member of the European Union has been thrown into fresh doubt by one of Brussels most senior officials.

On another testing day for the First Minister, European Commission Vice-President Viviane Reding backed comments suggesting a newly independent country would have to apply for membership.

Her views – in a letter to the Spanish Government – were seized on by opposition MSPs as the row over the First Minister's legal advice on the EU intensified.

Labour used a set-piece Holyrood debate to demand a full judicial inquiry into claims he lied about taking advice from the Lord Advocate during a television interview in March, although the call was immediately dismissed by the Government as "desperate".

The Scottish Tories voiced anger after the Lord Advocate turned down their request to appear before Parliament to explain his role in approving Government claims on Europe.

Mr Salmond, meanwhile, was criticised for snubbing the Holyrood debate to speak at renewable energy conference, with Labour MSP James Kelly accusing him of "breath-taking arrogance and contempt for the Scottish people".

The comments by Ms Reding, a commissioner from Luxembourg, emerged in Spain's El Pais newspaper.

In a leaked letter to the country's Europe minister, Inigo Mendez De Vigo, she backed his claim that even if Catalonia gained independence from Spain constitutionally "then such a state would not in any case form part of the EU".

Opposition MSPs said the remarks undermined Mr Salmond's claim that an independent Scotland would automatically be a member of the EU.

Scots Labour leader Johann Lamont said: "Alex Salmond and Nicola Sturgeon continue to assert Scotland will remain in the European Union but admit they have no real legal basis to back that up.

"Now we see further doubt cast on Scotland's place in the European Union by the Vice-President and Commissioner for Justice, Viviane Reding, who believes an independent Catalonia would be viewed as a new state in Europe.

"Why would Scotland be any different?"

Tory leader Ruth Davidson said: "Ms Reding makes it clear that should Catalonia, as an area within an EU member state, choose to secede from this state, it would have to re-apply as an accession state under article 49 of the EU Treaty.

"If that is true for Catalonia, the SNP has to explain why it would not be true for a separate Scotland."

Ms Reding's comments follow remarks by EC President Jose Manuel Barroso, who suggested an independent Scotland would be treated as a new state.

The Government last week announced it was now seeking specific legal advice on Scotland's EU membership.

In March, Mr Salmond told the BBC he had consulted the law officers on the issue "in terms of the debate".

He denied claims he lied during the interview, insisting he was speaking about general legal advice which "underpinned" all Government documents but agreed to a probe into separate allegations be broke ministerial rules.

A Scottish Government spokesman said: "As many legal and constitutional experts have confirmed, Scotland is part of the territory of the European Union and the people of Scotland are citizens of the EU – there is no provision for either of these circumstances to change upon independence."