THE direct cost to the taxpayer of the Scottish independence referendum is set to exceed £16m but the true total, including related and knock-on costs, may never been known.

In 2013 in an impact assessment for the Scottish Parliament, the estimated price-tag was set at £13.3m, a rise of £3m on previous figures, with the cost of running the referendum itself accounting for £8.6m with another £4.7m spent on regulation and campaign mailshots.

But since then, taxpayers have forked out more than £1.1m on Whitehall research, publications and private opinion polls alone as part of the UK Government's attempt to keep Scotland within the Union.

Equally, research and analysis for the Scottish Government, the centre-piece of which was the £800,000 White Paper, are estimated to have cost taxpayers at least another £1m.

However, there are other related costs too such as the many trips north of the border by UK Government Ministers in the months prior to polling day such as the Cabinet meeting in Aberdeen, which were to all intents and purposes referendum-related.

Plus, there are now the costs of the knock-on effects of the referendum result such as those for the Smith Commission, officials' work on producing the Coalition's options on English votes for English laws, the man-hours in Whitehall in drawing up the draft legislation for more powers for the Scottish Parliament together with future costs on the new Scotland Act.

In terms of research and presentation, the biggest expense incurred by the Lib-Con Coalition was for the 16-page booklet, What Staying in the UK Means for Scotland, published in June. This cost £723,501 and was distributed to 2.5m Scottish households.

Statistics from the Cabinet Office's transparency data for costs of more than £25,000, shows that the Cabinet Office's Devolution Team incurred costs for "market research attitudes in Scotland towards Scottish independence" undertaken by pollsters Ipsos Mori of £46,550 in January, £93,100 in March and £65,460 in April; a total of £205,110.

The Devolution Team also incurred costs for "communications support" from Engine Partners UK on three occasions; once in January for £30,605 and twice in April for £28,811 and £26,367; a total of £85,783.