John Swinney has been urged to deliver a Holyrood statement after a damning inquiry into the Edinburgh trams scandal questioned his “integrity” and accused him of meddling behind the scenes.

Lord Hardie finally published his findings into the Edinburgh trams fiasco yesterday, nine years and £13 million after it was announced by Alex Salmond’s government.

The investigation found that the costs of the project are likely to be around £835 million, significantly more than the £776 originally claimed by the City of Edinburgh Council. Together with the extension to finally complete the line to Newhaven, the costs have exceeded £1 billion.

The report pointed to a “litany of avoidable failures” and criticised the decision of Transport Scotland to walk away from the troubled project in 2007.

Read more: Edinburgh Tram Inquiry: John Swinney accused of meddling in crisis

The document pointed the finger at the city council, the company the local authority set up to deliver the tram project and Scottish ministers – putting particular blame on Mr Swinney, who was finance secretary at the time.

Mr Swinney quit as deputy first minister following the resignation of Nicola Sturgeon but remains an SNP MSP.

Lord Hardie, referring to Mr Swinney and Transport Scotland senior director Ainslie McLaughlin, said: “As with all witnesses who gave evidence in person, they testified on oath and their lack of candour calls into question their integrity.”

Transport Scotland walked away from the troubled project in 2007, with Lord Hardie concluding that in the following years, Mr Swinney was “directing” the city council “as to what should be done” to fix the crisis from behind the scenes.

Read more: Edinburgh tram inquiry reveals 'litany of avoidable failures'

Transport Scotland re-entered the project in 2011 to help conclude the fiasco.

Mr Swinney was scolded by Lord Hardie for attempting to “seek to exert influence in the background” after Transport Scotland had walked away.

The investigation reported that Mr Swinney met former Edinburgh Trams chairman David Mackay in February 2009 “regarding the ‘Princes Street Dispute’, when Mr Swinney told him to ‘get it sorted’”.

Lord Harvie agreed with evidence that this was Mr Swinney “pulling strings”.

Lord Hardie said that the “active involvement in the mediation and in the project after 2011 coupled with the activity of Mr Swinney” showed “just how far the Scottish ministers had moved from their stance in 2007”.

He added: “From seeking to distance themselves from major decisions on the project, they were now directing CEC as to what should be done.

The inquiry found that "there was no acceptable explanation provided" for the decision of Scottish ministers to "continue to fund the project to the extent agreed by their predecessors but to remove the safeguards to protect that funding".

Read more: Analysis: Was the Edinburgh Tram Inquiry pointless? Ask the businesses

Now, the Scottish Conservatives have called on Mr Swinney to make a personal statement to parliament after the accusations.

Lothians MSP Miles Briggs has written to the former finance secretary urging him to explain his role in the £1billion scandal.

Mr Briggs said: “Lord Hardie’s report contains eviscerating criticism of John Swinney and his role in the trams scandal – most notably his ‘lack of candour’.

“That’s why I have written to the former finance secretary urging him to make a personal statement in parliament on the issue.

“The public deserves an explanation for, and response to, the criticisms made of the SNP Government by Lord Hardie, given that this whole saga has cost the taxpayer in excess of £1 billion.

“John Swinney has serious questions to answer, and it’s in his interests to defend his actions.

“For such a senior figure in the SNP Government to have his integrity called into question is damning.”

The SNP has been contacted for comment.