The day-one Scottish currency proposal rests on the assumption that a new, untested currency can be introduced at or near full equivalence (parity) with sterling, with minimal disruption to wages, pensions, savings and debts. That assumption does not hold under standard economic conditions or historical experience. Scotland’s notional fiscal position under current arrangements shows a large structural deficit—£25.3 billion, or 10.9% of GDP, in the latest GERS figures. Combined with an external deficit, this is incompatible with markets treating a new floating currency as equivalent to sterling on introduction. Independent analyses (including from NIESR, the Institute for Government and macroeconomists such as Ronald MacDonald) have repeatedly indicated that an initial depreciation of 20–30% is a plausible outcome. That would immediately reduce the real value of incomes paid in the new currency relative to sterling-denominated liabilities. Around 900,000 Scottish mortgages (with tens of billions outstanding) and substantial corporate and public-sector debts remain denominated in sterling. There is no automatic conversion. If wages and public payments switch to the new currency while debts stay in sterling, a depreciation raises the local-currency cost of servicing those debts. Scottish Currency Group material itself notes that conversion of loans would be optional and would lag behind deposits; the risk of mismatch is therefore real and falls on households and firms. Import prices would also rise, feeding inflation and further eroding real purchasing power for those paid in the new unit. The Ireland comparison does not remove these problems. Ireland operated a currency-board arrangement fully backed by sterling assets, with explicit convertibility at par via the Bank of England acting as agent. Commercial banks held large sterling reserves. That self-backed parity lasted decades under conditions of high integration and sterling-area membership; it was not an unsupported free float. No equivalent institutional backstop or convertibility guarantee would exist for Scotland, and UK governments have long ruled out formal arrangements. Markets would price the difference immediately. Claims that money creation by a sovereign issuer removes these constraints overlook the binding limits of real resources, external financing and investor willingness to hold the new currency. A floating rate can adjust, but the adjustment occurs through lower real wages, higher debt-service costs and potential capital outflows precisely the effects on financial security that the proposal treats as secondary. The SNP’s own published policy of a transitional sterling period before any new currency “as soon as practicable” reflects recognition of these risks; the day-one alternative front-loads them without demonstrated preparation for the scale of the deficit or the debt stock. These are measurable exposures, not abstract theory. Any serious proposal must quantify the expected depreciation, the share of sterling liabilities that cannot be quickly redenominated, the inflation pass-through, and the institutional capacity to manage the transition. Wishful assertions of near-equivalence do not substitute for that analysis.