Mistakes made at the outset in the construction of two ferries delayed by over five years saw money “effectively wasted” on rebuilding units, the chief executive of Caledonian Maritime Assets Ltd (CMAL) said.

Kevin Hobbs claimed that the issues were down to a “catastrophic failure" of management, not a failure of the workforce.

The two vessels – the Glen Sannox and the as-yet-unnamed hull 802 – were originally due to be completed in 2018, but have since been delayed until at least 2023.

The delays have also seen the costs soar over budgets with the latest estimated cost reaching at least £250 million.

Mr Hobbs said units were “riddled with errors” which meant extra costs went towards undoing the work and rebuilding them.

It comes after former Ferguson Marine shipyard owner Jim McColl accused the company, which handles Scottish Government ferry contracts, of blocking every attempt to carry out an independent resolution.

Speaking at Holyrood’s Public Audit Committee, Mr Hobbs disputed claims that CMAL interfered in the work carried out in the Ferguson Marine, which runs the last remaining shipyard on the lower Clyde.

READ MORE: ScotGov-controlled CMAL 'got away with it' in Ferguson Marine ferry fiasco

He was asked to justify a statement in Cmal’s written submission, which claim the cause of the cost overrun was “catastrophic contractor failure”.

The chief executive said: “What we were seeing, basically, is units being built at risk, not signed off by us, not signed off by Lloyds and what that then meant was that when they were inspected there were many, many mistakes.

“So, Mr McColl said that we interfered. This is not interference. This is actually pointing out that this is a unit that has been built incorrectly.”

He said he rejected any claims of “meddling or interfering” in the construction, adding: “I think there was complete confusion by the shipyard.

“And let’s be honest about it, Mr McColl has no shipbuilding pedigree whatsoever.”

Explaining the skyrocketing costs, he said mistakes were made from the outset since the drawings for the vessels were not approved.

He said: “If you can imagine one unit of cost, it then takes a unit of cost to undo it, it then takes another unit of cost to do it properly.

“You can easily see that what should cost one unit of cost becomes three units of cost. That is the simplest way that I can explain what was going on.

“There were mistakes made at the outset by the builder because they didn’t have approved drawings and when the units were inspected they were riddled with errors and had to be undone and then redone.”

He added that the costs grew further if mistakes were not identified until the ships were already outside the shed or afloat, including for the Glen Sannox which was launched too early in November 2017.

The committee also heard that CMAL did not want to publicly announce Ferguson Marine as the preferred bidder to build two ferries at an event in 2015.

Nicola Sturgeon ultimately attended the event at the Port Glasgow shipyard on August 31, 2015 where Jim McColl’s company was declared the preferred bidder.

However, Cmal (Caledonian Maritime Assets Ltd) had advised against making a public announcement, saying discussions about the contract were ongoing and they did not want to present Ferguson Marine as a “fait accompli”.

Morag McNeill, interim chair of Cmal, said: “We were concerned it was going to be seen as a fait accompli with the public when we still had significant miles to go on the contract.”