Chancellor George Osborne says there's no legal reason the rest of the United Kingdom should share the pound with an independent Scotland if it votes to break away in a referendum this year.
"There's no legal reason why the rest of the UK would need to share its currency with Scotland," Mr Osborne said in a speech in Edinburgh on Thursday.
"If Scotland walks away from the UK, it walks away from the UK pound."
The Scottish National Party has claimed an independent Scotland would have the right to retain the pound and become part of a currency union with the rest of Britain.
But Mr Osborne said Scots need to be clear on the facts before making their biggest decision in three centuries in the referendum on 18 September.
"They are like the angry party to a messy divorce. But the pound isn't an asset to be divided up between two countries after a break-up as if it were a CD collection."
"The evidence shows it wouldn't work. It would cost jobs and cost money and wouldn't provide economic security for Scotland or for the rest of the UK," Mr Osborne said, waving a new Treasury analysis setting out the risks.
Opinion polls show separatists are lagging supporters of the union but the gap is starting to narrow.