The cost of finishing two delayed CalMac ferries originally contracted to Ferguson Marine has more than doubled, Derek Mackay has revealed.

In a ministerial statement, the finance secretary said "disastrous" mismanagement by the Port Glasgow firm, which was recently taken into public ownership, meant the original £97m contract was likely to end up costing close to £200m.

The boats are now expected to be about four years late, with an 80% chance they will be delivered in winter 2021 and autumn 2022 respectively, rather than the 2018 date originally planned for.

The two Caledonian Maritime Assets Ltd (CMAL) ferries have been hit by multiple delays, with the timing and costs part of a dispute between the Scottish Government and former shipyard owner industrialist Jim McColl.

A new assessment of the vessels by administrators has revealed costs have soared and their delivery will be delayed again.

The first ship, Glen Sannox, to serve on the Arran route, will not be ready until the tail-end of 2021 at the earliest.

The second ferry, known as Hull 802, is expected to be operational between July and August in 2022.

Around £83m of taxpayer's money has already been spent on the vessels to date.

The report, by Scottish Government-appointed turnaround director Tim Hair, predicts an extra cost of between £94.8m and £98.8m for remedial work and completion of the ferries

Mackay nationalised Ferguson shipyard earlier this month in order to safeguard the 350 jobs there and take over delivery of the CalMac ships.

Addressing MSPs, the finance secretary said: "The the failures of management, planning and process means the vessels are behind their original programme and that significant rework is required."

He added: "This report highlights why public ownership was the only option open to us to deliver these outcomes and why it was the right thing for the Scottish Government to step in when we did.

"In particular, the report sets out in stark detail the failings of the previous management and the impact that this has had on the condition and progress of the ferries being constructed at the yard."

Among the issues highlighted by Mr Hair's report areuncertainty over whether Ferguson marine had bought the necessary equipment for the ferries.

It found the basic initial design of the vessels has not yet been completed and approved by CalMac, another state-owned firm.

Mr Hair said internal processes "have generally been found to be poor or nonexistent to control a project of this magnitude".

Conservative MSP Jamie Greene hit out the government, saying: "It is an abject failure to deliver to our island communities new ferries on time or on budget.

"Beleaguered shipyard workers had their business put into administration as a result of the actions of this Scottish Government.

"The cabinet secretary, with no hint of irony, wants us to praise him for saving the yard which his own government put at risk of closure in the first place."

Mackay retorted: "If it were not for the actions of the Scottish Government, Ferguson's would not have a tomorrow."

Commenting on the announcement, GMB Scotland organiser Gary Cook said: "We have seen previous delivery dates missed because of failures in the way this contract has been managed and the botched procurement process.

"This highly skilled workforce now needs to be allowed to get on with the job."

"There remain questions to be answered about how the yard, and hundreds of jobs, came to be threatened by this debacle but we also need unity of purpose from management, the client and the Scottish Government."