MSPs have demanded to know why a key section of a document about the CalMac ferries scandal was withheld from them by the Scottish Government’s transport agency.

Holyrood’s public audit committee has asked Transport Scotland to supply it with the “complete version” of a letter sent by former minister Derek Mackay to an SNP MSP.

The committee has also asked the quango’s interim chief executive, Michelle Quinn, for “an explantation of the omission, at your earliest opportunity”.

It follows a row over incomplete evidence supplied to the committee by Transport Scotland on 28 October, which included a letter from Mr Mackay to Stuart McMillan in February 2015.

The committee in holding an inquiry into two CalMac ferries ordered from the Ferguson Marine yard on the Clyde in later 2015 for a fixed price of £97million.

The deal proved a disaster, leading to the yard being nationalised in 2019.

The boats - known as the Glen Sannnox and Hull 802 - are yet to be finished, but are so far £150m over budget and five years late.

It has already emerged that the state-owned ferry procurement body CMAL wanted to restart the bidding process because it had concerns about the order going to Ferguson Marine.

In particular, it was worrred about the year, then owned by one fo Nicola Sturgeon’s economic advisers, could not provide a standard industry guarantee to protect taxpayers in case the work was not completed.

However Transport Scotland, under instruction from the Government, pushed ahead, with Mr Mackay, the then minister for transport, signing off the order in October 2015.

The committee had asked Transport Scotland for any correspondence it had between the Mr Mackay and Mr McMillan, the yard’s local MSP, before the yard was made preferred bidder.

It emerged Mr McMillan had asked Mr Mackay if a builder’s refund guarantee  was required for the contract to be awarded to Ferguson’s.

In an indication that ministers might not insist on one, Mr Mackay replied saying that, while CMAL’s “preference” was for refund guarantees, “it has on occasion taken alternative approaches”, including for Ferguson’s under a different owner.

Although that part of Mr Mackay’s reply was given to the committee by Mr McMillan as part of his evidence, Transport Scotland’s.version of the same letter left it out.

In today’s letter to Ms Quinn, committee convener Richard Leonard said MSPs had been “concerned” that two paragraphs had been excluded from Transport Scotland’s evidence, and that “no attempt has been made to correct this omission”.

He went on: “Transport Scotland was given three weeks to return this information, with the offer to contact the clerks if the deadline date presented any difficulties. 

“In the year and a half I have been Convener of the Public Audit Committee, this is the only occasion I am aware of where repeated attempts were required to establish when this information would be received.

“The Committee would now ask you to provide a complete version of the former Minister’s letter, along with an explanation of the omission, at your earliest opportunity.”

In a separate letter, the committee has also ask Ms Sturgeon, who gave evidence on the deal in November, for more informationr, including asking for any minutes or notes taken as a result of a meeting she had with former Ferguson owner Jim McColl in May 2017.