Westminster's word is "final" and there will be no currency union for an independent Scotland, leading Scottish Lib Dem Danny Alexander said yesterday.

The Chief Treasury Secretary ruled out a deal to share the sterling before a bevy of pension fund managers in Edinburgh.

But economists have suggested the matter could already be out of Westminster's hands.

Tory Chancellor George Osborne and his Labour shadow Ed Balls have both explicitly ruled out a currency union under their governments in the event of a Yes vote in September's independence referendum

Scottish ministers have dismissed the rejection as a "campaign tactic," but Mr Alexander told the National Association of Pension Funds that the Westminster consensus was "final."

"[First Minister Alex Salmond] cannot honestly expect that Scotland would walk away from the rest of the UK, but taxpayers in England, Wales and Northern Ireland would still agree to stand behind the Scottish economy," he said.

Experts giving evidence to a backbench Holyrood committee on the issue this week have suggested however that the remainder of Britain may not have a choice.

Former World Bank economist Professor David Simpson told MSPs that it was "quite possible" for Scotland to keep the pound even without a formal agreement.

Ireland continued to use the pound until 1979, while Panama, Ecuador and El Salvador still use the US dollar today.

"Indeed this would not only be possible but, if Scottish interests alone were to count, it would be desirable. It would deliver the main benefits of a currency union of low transaction costs, no set-up costs, no exchange rate risk."

But University of Stirling professor David Bell said "dollarisation" would still leave Scotland without control over decisions like interest rates and the rate at which new money is printed.

Meanwhile credit would dry up as banks operating in Scotland could no longer rely on the Bank of England for a bailout in the next financial crisis - meaning jealous protection of their cash reserves.