A spike in the cost of ingredients since the EU referendum could lead to a "Brexit Irn-Bru tax", the Scottish Liberal Democrats have claimed.

Since the vote on June 23, manufacturers have had to deal with a jump in "imported inflation" for raw materials, with the soft drinks industry hit particularly hard.

Between June and July, inflation for imported ingredients used to produce soft drinks jumped by 6.3%, compared to a 1% increase between May and June, and over twice as high as any increase this year.

The industry employees around 15,000 people in the UK.

The British Soft Drink Association said ingredients likely to be imported include most fruit juices, citric acid, intense sweeteners, preservatives, vitamins and some colourings and flavourings.

The recipe for Irn-Bru, produced by A.G. Barr, is top secret but the Lib Dems have calculated that if only half of the ingredients the company use are affected by the increase, it could lead to a 6p increase in the cost of a two-litre bottle if the cost to be passed on to consumers.

Liberal Democrat MSP Mike Rumbles said: "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.

"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."

He added: "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."

A spokesperson for A.G. Barr told STV News: "Any business that buys products and services from abroad will be impacted to some degree by foreign exchange rate changes.

"We anticipate some higher input costs next year if the weakening of Sterling is sustained, however we are taking action to minimise any impact as much as possible and we will continue to ensure we provide our consumers with great tasting and good value products using the best ingredients."

The UK Government's new department for exiting the European Union said independence was the greater threat to the cost of Irn-Bru.

A spokesman said: "The UK Government will work hard to get the best deal when negotiating our future relationship with the EU.

"But the fact remains that the biggest threat to the price of Irn-Bru, and everything else in Scotland's shops, would be any threat of Scotland being taken out of its most important single market - the United Kingdom."

The Scottish Government said Brexit was "without doubt" the bigger threat to long-term prosperity.

A spokeswoman said: "Brexit is without doubt the biggest threat to Scotland's long-term economic success.

"Taking Scotland out of the European Union and our place in the world's biggest single market is projected to cost the Scottish economy up to £11.2bn per year by 2030, which is why the First Minister has made clear we must pursue all possible options for protecting Scotland's place in the EU."