SCOTTISH homeowners would face paying more for their mortgages and Scottish businesses more for their loans because an independent Scotland would fail to attract a triple A credit rating, it was claimed last night.

The doubts were raised by Michael Fallon, the Conservative backbencher, after he and fellow members of the Commons Treasury Committee were told by an expert that no newly independent nation had, to his knowledge, ever received a top-level triple A credit rating.

David Riley, managing director of sovereign and supra- national ratings at Fitch Ratings, one of three main credit rating agencies giving evidence to MPs yesterday, was asked by Mr Fallon if Scotland would still have a triple A rating should it break away from the UK.

Mr Riley was reluctant to give a direct answer, pointing out how the financial arrangements of an independent Scotland were not known and that there were many issues to be considered, such as monetary and banking arrangements. It would not be a straightforward division of assets and liabilities, he argued.

"So, there would be a huge number of factors that would influence what would be the rating," he said.

Pressed further by Mr Fallon, the executive from Fitch accepted that "history and track record" could be important in building credibility, but he declined to speculate because an independent Scotland did not have a set of national accounts.

Moritz Kraemer, from Standard and Poor's, and Alastair Wilson, from Moody's, took a similar view and declined to comment.

However, when Mr Fallon asked if there had been any other new nation given a triple A rating, Mr Riley replied: "Not that I am aware of. I'm fairly certain that has not been the case. I'm not aware of any situation where we have assigned a triple A rating to a new independent sovereign nation."

Last night, Mr Fallon told The Herald: "If Scotland became independent, it would be abandoning the comfort of the UK's triple A status and pay more for its money. There would be increased borrowing costs for businesses and it would put up people's mortgages."

Earlier this year, the issue of an independent Scotland's creditworthiness was raised when it was suggested the three main ratings agencies had indicated privately that a new sovereign state would not automatically inherit the UK's top-level rating and could expect to get one several notches below this level.

Finance Secretary John Swinney said he was confident an independent Scotland would still enjoy a triple A rating because "it was difficult to deny the effectiveness and strength of the economy".

l Opposition parties have stepped up the pressure on Alex Salmond to have a single question on the independence referendum ballot paper after an expert warned a second question would "muddy the waters".

Ron Gould, who reviewed the 2007 Holyrood voting shambles, said a single question would deliver a clearer outcome, while a two-question ballot would make the result "very difficult to determine".