The inquiry into the Edinburgh tram fiasco has so far cost £3.7m, it has been revealed, even though oral hearings yet to begin.

The revelation from Transport Scotland in response to a freedom of information request has led to an angry response from child abuse survivors who contrasted the concerns over the cost of the Scottish Child Abuse Inquiry, with the sums racked up by Lord Hardie's trams inquest in the two years since its launch.

When Susan O'Brien QC quit as chair of the abuse inquiry earlier this month, she claimed it was due to interference from the Scottish Government, and pressure on her panel over costs. These claims were corroborated by Professor Michael Lamb who had resigned a week earlier.

Members of In Care Abuse Survivors Scotland (Incas) said it was a double standard and accused deputy first minister John Swinney of penny-pinching over the abuse inquiry, and treating trams as more important than people.

Alan Draper, Incas parliamentary liaision officer, said: "The action of John Swinney can only be described as negligent , and he should offer his resignation. This will tell survivors that people are more important than trams."

"Lord Hardie has been allowed to proceed without interference , whilst the Goverment have grossly interfered with the Child Abuse Inquiry resulting in the resignation of two panel members," he said.

While calls for a judge to lead the child abuse inquiry had been ignored by the Scottish Government, Lord Hardie had been put in charge of the inquiry into the Edinburgh trams project, which cost £776m and was completed five years late.

Mr Draper said there was a lack of scrutiny of the £3.7m spent by Lord Hardie's team, while senior figures in the child abuse inquiry - which has so far cost £1.8m - claim their independence has been routinely compromised.

"Susan O'Brien was effectively dismissed by John Swinney, who did not bother to consult survivors, or consider the impact that this would have on survivors," he added. "It would appear that trams are more important than human beings who suffered years of abuse."

He said the government needed to understand that many of those who suffered abuse as children in residential homes and other care settings needed recognition of their suffering and suitable redress for the physical and emotional scars incurred. "If you slip on a pavement, caused by negligence , you will be compensated, " he said.

"If you suffer years of abuse, you have to fight the government and provider agencies to even get a simple acknowledgement . The time has come for the government to get its priorities right .

The trams inquiry was set up in 2014 by then first minister Alex Salmond.

It is looking at the project, examining its governance, management and other areas to try to find out why it was delayed and why it ''cost considerably more than originally budgeted for and delivered significantly less than was projected through reductions in scope'', according to its remit.

It is not known when Lord Hardie will report his findings.

Figures published by Transport Scotland in response to a BBC freedom of information request revealed a total of £3,708,000 has been spent on the inquiry already.

A breakdown of the costings shows £1,822,000 has been spent on staffing, £502,000 on accommodation costs, £716,000 on legal fees, £540,000 on IT costs and £128,000 on miscellaneous costs.

The trams began operating at the end of May 2014 after six years of disruption and a long-running dispute between Edinburgh City Council and contractors.

The Scottish Government has agreed to continue to fund the costs of the inquiry until its completion.

A spokesman said: "We have been clear from the outset that the inquiry should be efficient and cost-effective, however we know that major infrastructure projects do generate large quantities of documentation and we understand the inquiry team has already gathered over six million documents.

"Lord Hardie and his team is firmly committed to discerning the facts in a robust and thorough manner."

A spokeswoman for the Edinburgh Tram Inquiry said: "The Scottish Ministers have been clear from the start that the Inquiry should be timely and cost effective."