Douglas Ross said emails showed John Swinney’s approval over the much-debated Ferguson Marine ferries contract was “essential” during a heated First Minister’s Questions (FMQs) on Thursday.
The SNP have been under continued pressure after an Audit Scotland investigation found the contract for two delayed and overbudget CalMac ferries was approved by ministers without normal financial safeguards. The ships, still being built at the Port Glasgow yard, will be five years late and could cost more than £250m.
Civil service advice in an email chain revealed the Deputy First Minister had sight of the deal.
Focusing in on the email chain during FMQs, the Conservative leader said "honest John charged ahead” with the contract despite clear risks.
Mr Ross said: “Against overwhelming evidence, John Swinney signed off the deal anyway. It seems obvious to everyone what happened here - the SNP wanted the political praise for keeping the yard open ahead of an election so they ignored all of the alarm bells.
"It looks a lot like the SNP made a dodgy deal and are trying to cover it up.”
However, the deputy First Minister said Mr Ross is “smearing and inventing” information.
John Swinney said he takes "collective responsibility" over ferries contract but said the decision was made by Derek Mackay, the then minister for transport.
The deputy first minister denied the ferries contract was motivated by political gains.
“There was no political motive behind this contract,” Mr Swinney said, “The objective of this Government was to ensure that ferries were built and that’s what we’re concentrated on achieving and we are also determined to ensure that the employment in the lower Clyde was supported with contracts coming from the CalMac network.”
The minister said the email Mr Ross cites is referring to a brief on the ferries contract decision which was already taken.
Mr Swinney added: “The people will see through his (Ross’) grubby tactics today.
"My role was to provide the necessary budget for building the ferries.
"After the final decision was taken officials briefed me about the contract being awarded and assured me on the basis of the contract the budget I had approved in 2015 did not require to be changed.”
Mr Swinney’s comments came just hours after Roy Brannen, the interim Director General of Net Zero in the Scottish Government, told the Public Audit Committee the decision to award a contract was taken “entirely” by the former transport minister Derek Mackay.
The senior civil servant told MSPs: "Given all we were procuring at that time and bearing in mind we had around £2 to £3 billion worth of work underway with Queensferry Crossing, the M8, 73, 74, Aberdeen Western Peripheral, the ferries contract would have been entirely the decision for the minister for transport. ”
Mr Brannen, the former Chief Executive of Transport Scotland, also told MSPs John Swinney and Nicola Sturgeon had no role in approving the ferries contract.