The former Chancellor, now head of the pro-UK Better Together campaign, warned there were no guarantees the Nationalists' scheme would be accepted and, if it was, would come with "massive strings attached".
In his most comprehensive critique of SNP policy to date, he also questioned its claims on EU membership and warned Scots could no longer claim British culture as their own if they left the UK, declaring: "British music will no longer be our music."
Alex Salmond and Nicola Sturgeon have claimed that an independent Scotland would be welcomed into a currency union with the UK, with the Bank of England as its shared central bank and lender of last resort.
But Mr Darling said: "No one has asked the rest of the UK whether or not they would agree to this – it's simply asserted. Why should the rest of the UK agree to a currency union without being asked?
"But the most obvious problem with the common currency is that sooner or later it takes you to economic and then political union.
"Scotland would leave the UK only to end up in the same place as it began, with all the trauma that would entail."
Warning that Scotland would have to hand back economic levers to a foreign neighbour, he added: "It is a nonsense."
The criticisms were a direct riposte to Mr Salmond's speech to the SNP conference, in which the First Minister pledged to end the "nonsense" of Scotland belonging to the UK.
It came as Mr Darling delivered the John P Mackintosh lecture in East Lothian, given annually in memory of the former Labour MP and champion of devolution.
A spokeswoman for the pro-independence Yes Scotland campaign said: "It is a straightforward matter for Scotland to retain the pound after independence. It makes sense for Scotland to share a currency with our biggest trading partners and it also makes sense for the rest of the UK."