THE cost to the taxpayer of staging next year's independence referendum will be £13.3 million –  a third higher than previously estimated.

Referendum minister Nicola Sturgeon said running the poll, including staffing polling stations and organising the count, will cost £8.6m.

Overseeing the campaign and raising public awareness, including giving Better Together and Yes Scotland a free mailshot to every voter in the country, will come to a further £4.7m.

Previous estimates put the total referendum cost at £9m-£10m.

The new figures were confirmed in a business and regulatory impact assessment of the Referendum Bill going through Holyrood.

The routine study, required by all new legislation, said returning officers were expected to incur costs of £8.6m, which will be paid directly by the Scottish Government. The move "should ensure that there is no extra pressure on local authority budgets as a result of the bill", the assessment said.

The additional £4.7m will include the costs of the Electoral Commission, the independent watchdog that will police the campaign.

Its role includes ensuring the two main campaign groups, Better Together and Yes Scotland, and the various political parties, do not spend beyond strict legal limits set out in the bill.

The Electoral Commission is answerable to the Scottish Parliament, which will meet its costs. However, the Scottish Government will give Holyrood extra cash for the purpose to make sure the referendum does not hamper the work of parliament.

Ministers will also pay for a mailshot from the two main campaign groups to every voter in the country in the run-up to the vote on September 18 next year.

In its Your Scotland, Your Referendum consultation published in January last year the Scottish Government said: "The total cost of the referendum is likely to be around £10m, the bulk of which will be spent on running the poll and the count.

"This cost is broadly in line with the cost (per voter) of the Welsh Assembly and AV referendums in 2011. There will be no public funding for campaign organisations."

Scottish Labour's constitutional spokeswoman Patricia Ferguson MSP said: "So we now know that the cost of the SNP's constitutional obsession is around £13m.

"The price-tag is substantial and doesn't include the costs to Scottish families of sorting childcare or taking time off work due to schools being closed for the vote.

"As our economy continues to stutter along, all the effort is going into winning the battle to break up Britain. The absolute focus of the Government should be on getting Scotland growing again. Alas, even that is neglected on the altar of separation."

Scottish Conservative deputy leader Jackson Carlaw said: "This is the cost we know of to allow the SNP to carry out its separation experiment.

"What isn't detailed is the price of all the uncertainty caused by this referendum since 2011."

As part of the impact assessment, Ms Sturgeon said: "A large majority of respondents to the Your Scotland, Your Referendum consultation were in favour of holding a referendum, mostly on the grounds that it is the democratic right of the people of Scotland to have their say on their country's constitutional future."