IF we had a pound for every time we've heard this one, we'd pay people to stop repeating it – because it's patently untrue.

Of the 28 current EU member states, 19 use the euro. That was introduced for electronic transactions in 1999, then in cash form three years later, with 12 countries involved at first. The plan was to make cross-border trade easier and create economic stability. However, two member states – the UK and Denmark – negotiated opt-outs and seven others are outwith the euro as they do not fulfil criteria to join.

According to the EU's own website all member states, with the exception of those with opt-outs, are "required to adopt the euro and join the euro area", having first met "convergence criteria".

But there is no timetable for this, and half of the 13 nations that have joined the EU since 2004 are still not on board.

One of the preparatory steps for adopting the euro is membership of the Exchange Rate Mechanism (ERM) for at least two years. That step, as explained to Kay Burley of Sky News by the SNP's Ian Blackford in a broadcast that went viral, is "entirely voluntary". He said: "You can't be forced into the euro against your will. The last three countries that have joined the EU have not joined the euro."

What is the ERM anyway? In the words of the European Commission, it ensures exchange rate fluctuations between the euro and other currencies within the EU don't "disrupt economic stability". EU members not using the euro can peg their currency to it, with the value of their system allowed to rise and fall within certain boundaries.

While the EU says member states are "expected to participate" in the ERM, it is emphasised that "participation in ERM is voluntary for non-euro countries with an opt-out from the single currency".

Scotland could, if it wanted, seek to negotiate an opt-out, or do as Bulgaria, Romania and Croatia have done and take its time over potential eventual membership – none of them have as yet joined the ERM. After all, the EU says it is "up to individual countries to calibrate their path towards the euro".

Under this policy, an independent Scotland within the EU could seek to retain its own currency indefinitely. That could be sterling, as now, but at the recent SNP conference, delegates voted to make the introduction of a new Scottish currency the party's official policy. Under that plan, the timing of the switch would be determined by six economic tests.

European Commission President Jean-Claude Juncker has said he has "no intention of forcing countries to join the euro if they are not willing or not able to do so".

And there's a solid example of this in the case of Sweden, which became an EU member state in 1995. It still uses the krona – and it's still not a member of the ERM.

Politicians asked the public there if they wanted to join the currency union in 2003, a question which was answered with a “no”.

What we do know about the immediate economic future for Scotland is that we are braced for a hit as the UK pulls us out of Europe – the only question is how big that will be. Scottish businesses exported £14.9 billion worth of goods and services to the EU in 2017, with successful trade deals taking that figure up by more than 13% in just one year. It is thought that leaving the bloc could cost us around £16bn a year.

WHAT TO SAY

A new EU nation would have to make a notional commitment to joining the euro at some point – but there’s no timetable or any pressure to do so. Only 19 of 28 current members use the euro, and Sweden still isn’t in after 24 years. An independent Scotland could choose to join the euro, or hold on to its own currency indefinitely – we’d have the power to make that choice.

This article is part of our BUSTED supplement, debunking nine Unionist myths about Scottish independence. It was made possible by support for our 10,000 Steps campaign – if you haven't yet subscribed to The National, click here to find out how it'll help us boost the case for Yes directly.