Shipyard bosses were “fairly and squarely” to blame for the calamitous delays and costs overruns at Ferguson Marine, it has been claimed.

Kevin Hobbs, chief executive of Caledonian Maritime Assets Ltd (CMAL) – the government body which placed the order for two new ferries at the yard – also said he was “desperately upset and desperately concerned” that they were still not ready.

An inquiry into the debacle by Holyrood’s Rural Economy and Connectivity Committee will begin hearing oral evidence next week.

Ferguson Marine shipyard, which was acquired by tycoon Jim McColl’s Clyde Blowers empire in 2014, was nationalised last year after collapsing into administration in the wake of the dispute.

At the weekend, Mr McColl – who blames CMAL – said he wanted to give evidence at the inquiry “and be questioned under oath, as everyone who gives testimony to it should”.

He also raised concerns that several former Ferguson Marine executives would not be able to take part in the probe as they had signed non-disclosure agreements (NDAs) with the Scottish Government.

The two CalMac ferries at the centre of the row are £100 million over budget and will now be around four years late.

In an interview with the BBC, Mr Hobbs dismissed previous claims by Mr McColl as “urban myths”. He said the dual-fuel ferries were not “prototypes” and rejected claims that CMAL had made “hundreds if not thousands” of design changes.

He said: “That simply did not happen.” Mr Hobbs also said Ferguson started building the ferries before the design stage was finished.

He said: “Very simply, the design was still going on when the steel cutting was happening and effectively the shipyard was designing the vessel and building the vessel at risk, and that was a fundamental flaw.”

Elsewhere, he told the BBC that a £66m compensation claim against CMAL by Ferguson last year was “basically a work of fiction”.

He added: “We refuted that in its entirety and in my career I have never, ever seen that happen before.” Mr McColl previously claimed the two CalMac ferries should be scrapped and started again.

He said the ships would take longer to complete than the Scottish Government said, while costs could rise further.

He added: “You’d be better building from scratch and to a design that’s more suited to what’s needed. They could probably build three smaller vessels for less than £100m and it would give them more flexibility.”

Mr Hobbs dismissed this as “totally incorrect”. Finance Secretary Derek Mackay told MSPs in December that the final cost of sourcing the vessels from what is the last civilian shipyard on the Clyde would be around double the original “fixed price” contract of £97m.

He blamed “disastrous” mismanagement by the previous owners. There is now an 80 per cent chance the boats will be delivered in winter 2021 and autumn 2022 at the earliest, instead of mid-2018 as planned.

The first ship is destined for the Arran route, the second for Skye, Harris and North Uist.

A detailed report undertaken by the new management team at the yard previously said there had been a lack of project management on the contract, with no single person understanding it all. Basic design work remained incomplete after almost five years, with jobs done out of sequence, leading to “significant rework”.

Meanwhile, specification changes meant most of the pipework in an engine room had to be removed.

Storage of materials and stock-taking had also been inadequate, and it was unclear “whether sufficient stock exists to complete the project”. The two vessels had also been poorly cared for, with equipment damage and rainwater ingress.

The report concluded the total future cost of delivering the vessels would be between £110.3m and £114.3m. The Scottish Government has also written down £45m in loans to the yard, setting their value at “nil” in its accounts, taking the total potential overall cost to a quarter of a billion pounds.