Bank of England governor Mark Carney has issued his strongest warning yet against a currency union, saying it would be "incompatible with sovereignty" and raising the prospect it could lead to a eurozone-style economic crisis.

His comments came as experts warned independence could be "cataclysmic" for the UK economy.

Japan's largest bank Nomura warned the value of the pound could fall by as much as 15% if there is a Yes vote next week.

Jordan Rochester from the bank warned that a lot of money could be pulled from the UK amid uncertainty over the effects independence, adding: "These are scary times."

Taking questions after a speech to the TUC conference in Liverpool, Mr Carney said any currency union would require free trade, a banking union and the agreement of the rest of the UK to bail out Scotland's banks in any future banking crisis.

He said: "You only need to look across the channel to see what happens if you don't have all of those components in place."

He also pointed to Labour, the Conservatives and the Liberal Democrats' pledge to refuse to enter a sterling zone with an independent Scotland.

He said in that context that "a currency union is incompatible with sovereignty".

First Minister Alex Salmond has insisted that the pro-UK parties are bluffing when they say they would block a sterling zone.

The SNP leader has said it would be in the economic interests of the remaining parts of the UK to share the pound with a resource-rich Scotland.

He has also proposed an independent Scotland would have a member of the Bank of England's monetary policy committee, to argue in Scotland's interests.

But recent polls suggest that public opinion across the rest of the UK opposes any sharing of the pound in a formal union.

Under pressure on the issue, Mr Salmond claimed earlier this month to have three Plan Bs on an independent Scotland's currency.

But he has also insisted that Scotland cannot be prevented from using the pound - a move widely seen as a hint he is considering so-called sterlingisation, in which Scotland would use the currency with no input on its economic levers, such as interest rates.

Earlier this week George Osborne repeated that warning "no if, no buts, we will not share the pound".

Better Together leader Alistair Darling said: "Mark Carney has confirmed what we have been saying all along - a currency union is not compatible with sovereignty.

"It would mean what would then be a foreign country having control over our economy. That's why a currency union would be bad for Scotland, as well as the rest of the UK.

"What Scots deserve now from Alex Salmond is honesty about what his Plan B is. Would we rush to adopt the Euro? Or would we set up a separate unproven currency?

"This really matters to families in Scotland. The reaction of the markets yesterday showed just how damaging the uncertainty over currency is for Scotland. It puts jobs at risk. It means a weaker economy and less money to spend on our NHS.

"We don't have to take on all these risks. We can have more powers for Scotland guaranteed, without taking on all the risks of separation. It's the best of both worlds.

A spokeswoman for Scottish finance secretary John Swinney said: "Governor Carney made a full statement back in January on the arrangements that would be required to establish a successful currency union, including reaching shared agreements on certain elements of sovereignty such as overall debt levels.

"All of these issues were considered in detail by the Fiscal Commission, which includes two Nobel laureates, and concluded that a currency union was in the best interests of both an independent Scotland and the rest of the UK.

"The Governor has made clear that the bank is ready to implement whatever is decided.

"Successful independent countries such as France, Germany, Finland and Austria all share a currency and they are in charge of 100 per cent of their tax revenues, as an independent Scotland would be. At present under devolution, Scotland controls only 7% of our revenues.

"The political position of the three Westminster parties -which Governor Carney noted today - will of course change after a Yes vote. And as the momentum builds behind the Yes campaign, their currency bluff has well and truly been called."

Meanwhile, uncertainty over the outcome of the referendum continued to affect the pound.

The FTSE 100 Index, which struggled yesterday following big losses for firms with Scottish links, was 5.8 points lower at 6829, while the pound was just above 1.60 against the US dollar after big losses on Monday took it to a 10-month low. The pound was down against the euro, at 1.25.

Asked yesterday about "panic" in the markets on Monday, Mr Salmond countered that shares in Scottish companies including Aberdeen Asset Management and Aggreko had risen the next day.

He added: "What George Osborne has done is reinvented more powers for the Scottish Parliament that two days later we see as an empty gesture. When markets see that sort of panic, they see a Westminster government with no contingency plans."