Drinks makers such as Cumbernauld-based AG Barr are already seeing higher ‘imported inflation’ for raw materials, although these have yet to be passed onto shoppers, Lib Dem MSP Mike Rumbles said today. Ingredients costs for soft drinks products jumped a huge 6.3% between June and July, compared to only 1% between May and June.Although the recipe for Irn Bru is a famously well-guarded secret, if just half the ingredients were affected by the increase, the Lib Dems say it could lead to a 6 pence increase in a standard two litre bottle if passed onto consumers.Mr Rumbles said: “Scots face the prospect of a Brexit Irn Bru tax if AG Barr can’t keep their costs down.“Millions of businesses that use imported materials are already facing higher costs as a result of Brexit. If we abandon full membership of the Single Market, as some Ministers have proposed, then things will only get worse.“I am sure that companies like AG Barr will be crunching the numbers and doing their best to protect their customers. But they are not helped by a Tory government that is flat out refusing to tell us anything about what they think Brexit would look like or whether membership of the Single Market is under threat.”The higher costs are likely to get even worse if the UK does not secure full membership of the EU Single Market, Mr Rumbles warned..Mr Rumbles added: “When Boris and his pals were telling us about the brave new world that Brexit would bring they failed to mention that Scots could see the price of our favourite soft drink increase."A spokesman from AG Barr admitted the fall in the value of the pound since the Brexit vote has had an impact.