This is almost an identical sum to the Iraq Inquiry, which, according to its own most recent estimate, had cost £13,126,900 by the time it published its 12-volume report in 2016.
The inquiry into the Edinburgh tram project is examining why the venture finished five years late and cost £776 million, twice as much as initially planned, despite its significantly shorter route.
However, more than eight years after the probe was ordered by the former first minister, Alex Salmond, who wanted it to be “swift and thorough”, it has yet to produce itsreport.
The Scottish Government’s Budget for 2022/23 set aside another £500,000 for the inquiry, suggesting that, if it is not completed this year, it could exceed the cost of the Iraq Inquiry.
Lord Hardie, the former Lord Advocate leading the tram inquiry, has made it clear he will not be rushed and the process will take “as long as is necessary”.
The latest figures on its costs, provided following a Freedom of Information request, show the vast majority of the £13.1m has been spent on staff and legal fees.
Staff costs are due to reach £6,100,262 by the end of this financial year, while legal fees are projected to hit £3,076,224 – a combined total of £9.1m.
A further £1,384,121 is expected to have been spent on IT system costs, as well as £868,859 on rent for office facilities and £419,928 on the inquiry’s media team.
Edinburgh City Council transport convener Scott Arthur said the inquiry had become a “source of frustration and embarrassment in Edinburgh”.
“The time taken has undermined the credibility of the inquiry, and the money spent by the SNP Government on this is a source of anger,” he said.
Scottish Conservative local government spokesman Miles Briggs said people would be “astounded” the inquiry had cost the same amount as the Iraq war investigation.
“It shouldn’t be too much to ask for Edinburgh residents to get the answers they deserve out of this inquiry, while also delivering value for money for the taxpayer,” he said.
A spokeswoman for the Edinburgh Tram Inquiry said: “The inquiry’s evidential database contains over three million documents that have to be carefully considered, which is an extensive, but vital task.
“We continue to make good progress towards producing the report and recommendations, which will be published as soon as practicable.”
A Transport Scotland spokesman said: “We have agreed to continue to fund the costs of the Edinburgh Tram Inquiry until it is completed. Final costs will be published when they become available. Staffing matters, including how many people the inquiry employs and how much they are paid, are a matter for the inquiry.”