An independent Scotland would be economically "subordinate" to the rest of the UK and lose its coveted triple-A rating, an economic expert has warned.

Martin Wolf told MPs Scotland would not be "equal" to the remainder of the UK if it kept the pound.

The former SNP adviser told the Commons Scottish Affairs Committee that other European countries would try to block Scotland introducing low corporation tax rates. And Professor John Kay, a former member of the Scottish Government's Council of Economic Advisers, said EU members were "not going to let (reducing rates) happen".

However, the SNP rejected their comments and said it was "confident" Scotland would have the top credit rating.

Debate over what effect independence would have has raged for months. The UK has the top rating, the so-called triple-A.

However, last month one ratings agency threatened the UK with a downgrade amid fears over stalling growth and exposure to the struggling eurozone.

Mr Wolf told MPs that as a new country, and one exposed to "vola- tile" oil revenues, credit ratings agencies would treat Scotland cautiously. He said it was "extremely unlikely" an independent Scotland would keep the triple-A rating, although he also warned the UK "was on the margin". A lower rating would result in a higher cost of borrowing, he told MPs.

Prof Kay, visiting Professor of Economics at the London School of Economics, appeared to back that stance but said he did not think the resultant borrowing costs would be "massively higher".

He said he thought it unlikely Scotland would have a "better" credit rating than the UK. Both men said they thought EU countries would step in to prevent Scotland setting a low rate of corporation tax rate, like that seen in Ireland.

They would veto such a move as part of negotiations for Scotland to join the EU, they said.

Stewart Hosie, the SNP Treasury spokesman, said the SNP was "entirely confident" an independent Scotland would have the top credit rating. "That position is supported by Scotland having stronger public finances than the UK as a whole, and lower public sector debt," he said.

Claims EU countries might try to block Scotland's plans for corporation tax were based on a "fundamental misunderstanding of Scotland's status, he added.

"An independent Scotland will not be an accession state to the EU but a successor state."

However, Margaret Curran, the Shadow Scottish Secretary, said the evidence was "powerful".

l Fitch said it is lowering its outlook for the United Kingdom, indicating a downgrade from its Triple A status may be coming.

While the UK is well positioned now, it has very limited ability to absorb any further economic shocks stemming from the European crisis, the ratings agency said.