Independence could burden Scottish companies with more than £1 billion of extra costs, a report commissioned by local engineering firm Weir Group said yesterday, adding fuel to the business case against a split.

The 80-page report researched by forecasting and analysis group Oxford Economics found a new Scottish currency could cost local businesses and households £500 million a year in transaction costs with a further one-off cost of £800 million for the transition.

Scotland will vote on September 18 on whether it should remain part of the UK and business leaders have raised concerns over currency, tax, regulation and membership of the European Union if the country gains independence.

The potential loss of the pound is one of the biggest fears for businesses in Scotland. All three main UK political parties have ruled out a shared currency despite this being the Scottish government’s preferred option in light of a “yes” vote.

The report said a new, free-floating Scottish currency could have a more volatile exchange rate given Scotland’s dependence on oil and gas and the financial sector.