The Confederation of British Industry has launched a scathing attack on the Scottish National Party's economic plan, in the event the country breaks away from the UK, by saying it "doesn't add up."

The CBI said in a detailed report that, even taking into account oil and gas revenues, the SNP's economic plans and promises do not make sense, when looking at the numbers.

"The minute you draw a line between Gretna and Berwick, Scotland starts to drift apart from its biggest market and loses a significant amount of economic clout," said John Cridland, CBI Director-General.

"The economic plan outlined in the (SNP's) White Paper does not add up. It ignores the need for deficit reduction, instead promising more unfunded spending.

"On the key issues that are critical to jobs and growth, the White Paper's lack of clarity runs the risk of jeopardising an independent Scotland's future success."

Scottish people will vote in an independence referendum on 18 September this year and will be asked the straight "yes/no" question: "Should Scotland be an independent country?"

The SNP has repeatedly promised voters that if it breaks the 307-year union with England, it will retain the pound, stay a member of the European Union, and still share a financial industry regulators and laws.

"Independence would force Scotland's major industries to grapple with two lots of red tape and lead to Scots facing higher borrowing costs on loans, mortgages and credit cards," said Cridland.

"Keeping the pound is the best option for Scotland but that is only on offer through maintaining the union. The main UK political parties have ruled out currency union as an option, so we're calling on the Scottish Government to set out a credible plan B.

"An independent Scotland would also have to negotiate hard to get back into the EU, temporarily losing access to the world's biggest trade area with huge economic consequences.

"Scotland's economy is a real success story as part of the UK – it has the independence and flexibility of devolution alongside the support of the union. The fate of Scotland is, of course, a decision for the Scottish people, but business is clear - we are stronger together."